CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 SPACECRAFT_NAME = MAGELLAN TARGET_NAME = VENUS OBJECT = TEXT PUBLICATION_DATE = 1993-04-01 BYTES = 80 NOTE = "MAGELLAN ARCDR CUMULATIVE RELEASE NOTES" END_OBJECT = TEXT END ======================================================================== RELEASE NOTES FOR THE CURRENT ARCDR DISK (see below for information about previous ARCDR products) +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.00541-00600;5 | MGMORB FIT33 | | MG_2018 | ARCDR.00601-00660;5 | Jan 6, 1993 | | | ARCDR.00661-00720;5 | using orbits 376-5747 | | | ARCDR.00781-00840;4 | | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 0565-0676 | partial loss | partial loss | DTR-A failure | | 0677-0786 | no data | no data | Superior conjunction | | 0787-0840 | partial loss | partial loss | DTR-A failure | | 0788 | no data | no data | Not reprocessed | | 0814 | no data | no data | DSN outage | | 0815 | partial loss | partial loss | DSN outage | | 0822-0824 | no data | no data | Not reprocessed | 0825-0826 | no data | no data | Spacecraft anomaly | | 0827-0828 | good data | partial loss | Bad antenna pointing | +-------------+--------------+--------------+--------------------------+ This disk contains data from orbits 565-676 and 787-1059 that were ori- ginally published on disks MG_2002 and MG_2003. The gradual failure of an on-board data recorder (DTR-A) corrupted up to 50% of the down-link telemetry from each orbit. These data have now been partially recovered and the altimetry and radiometry data re-analyzed, increasing the number of footprints by about 10%, the number of radiometry footprints by 25%, and greatly improving the quality of the remainder that had been record- ed on DTR-A. Data from orbits 788 and 822-824 were not re-processed. The original ARCDR files are located on MG_2003. See also the comments on the original disks, MG_2002 and MG_2003, below. ======================================================================== COMMENTS ON PREVIOUS ARCDR PRODUCTS +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.04501-04560;1 | | | | ARCDR.04561-04620;1 | | | | ARCDR.04621-04680;1 | | | | ARCDR.04681-04740;1 | | | | ARCDR.04741-04800;1 | | | | ARCDR.04801-04860;1 | MGMORB FIT33 | | MG_2017 | ARCDR.04861-04920;1 | Jan 6, 1993 | | | ARCDR.04921-04980;1 | using orbits 376-5747 | | | ARCDR.04981-05040;1 | | | | ARCDR.05161-05220;1 | | | | ARCDR.05221-05280;1 | | | | ARCDR.05581-05640;1 | | | | ARCDR.05641-05700;1 | | | | ARCDR.05701-05760;1 | | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 4503-4507 | no ar_rho | partial loss | Low downlink SNR | | 4511 | no data | no data | Low downlink SNR | | 4512-4513 | no ar_rho | partial loss | Low downlink SNR | | 4524-4528 | no ar_rho | partial loss | Low downlink SNR | | 4533-4534 | no ar_rho | partial loss | Low downlink SNR | | 4543-4547 | no ar_rho | partial loss | Low downlink SNR | | 4548 | no data | no data | Low downlink SNR | | 4551-4552 | no ar_rho | partial loss | Low downlink SNR | | 4555 | no ar_rho | partial loss | Low downlink SNR | | 4563-4568 | no ar_rho | partial loss | Low downlink SNR | | 4567-4569 | no data | good data | VV-polarization test | | 4570-4571 | no data | no data | Low downlink SNR | | 4572-4574 | no data | good data | VV-polarization test | | 4575-4584 | no ar_rho | partial loss | Low downlink SNR | | 4585 | no data | no data | Low downlink SNR | | 4586-4587 | no ar_rho | partial loss | Low downlink SNR | | 4588 | no data | no data | Low downlink SNR | | 4589-4591 | no ar_rho | partial loss | Low downlink SNR | | 4592-4597 | no data | no data | Low downlink SNR | | 4600-4609 | no ar_rho | partial loss | Low downlink SNR | | 4610 | no data | no data | Low downlink SNR | | 4611 | no ar_rho | partial loss | Low downlink SNR | | 4612-4619 | no data | no data | Low downlink SNR | | 4620-4621 | no ar_rho | partial loss | Low downlink SNR | | 4622-4624 | no data | no data | Low downlink SNR | | 4625 | no ar_rho | partial loss | Low downlink SNR | | 4627 | no data | no data | Low downlink SNR | | 4629-4631 | no data | no data | Low downlink SNR | | 4632-4634 | no ar_rho | partial loss | Low downlink SNR | | 4635-4638 | no data | no data | Low downlink SNR | | 4639-4643 | no ar_rho | partial loss | Low downlink SNR | | 4644-4732 | no data | no data | Low downlink SNR | | 4733-4985 | no data | partial loss | ALTA not nadir-pointing | | 4739 | no data | no data | Gravity mapping only | | 4742 | no data | partial loss | Low downlink SNR | | 4747 | no data | no data | Gravity mapping only | | 4748-4749 | no data | no data | Low downlink SNR | | 4755 | no data | no data | Gravity mapping only | | 4763 | no data | no data | Gravity mapping only | | 4771 | no data | no data | Gravity mapping only | | 4773 | no data | no data | Low downlink SNR | | 4775-4778 | no data | no data | Low downlink SNR | | 4779 | no data | no data | Gravity mapping only | | 4785 | no data | no data | Low downlink SNR | | 4787 | no data | no data | Gravity mapping only | | 4789 | no data | no data | Low downlink SNR | | 4790 | no data | partial loss | Low downlink SNR | | 4795 | no data | no data | Gravity mapping only | | 4803 | no data | no data | Gravity mapping only | | 4808 | no data | no data | Low downlink SNR | | 4810-4812 | no data | no data | Low downlink SNR | | 4819 | no data | no data | Gravity mapping only | | 4826-4829 | no data | no data | Low downlink SNR | | 4835 | no data | no data | Gravity mapping only | | 4836-4837 | no data | no data | Low downlink SNR | | 4842 | no data | no data | Low downlink SNR | | 4843 | no data | no data | Gravity mapping only | | 4847-4848 | no data | no data | Low downlink SNR | | 4851 | no data | no data | Gravity mapping only | | 4878-4881 | no data | no data | Low downlink SNR | | 4887-4888 | no data | no data | Low downlink SNR | | 4898-4900 | no data | no data | Low downlink SNR | | 4919-4921 | no data | good data | High-Res Altimetry Test | | 4923-4927 | no data | no data | Low downlink SNR | | 4930-4932 | no data | no data | Low downlink SNR | | 4835 | no data | no data | Low downlink SNR | | 4953 | no data | no data | Low downlink SNR | | 4956 | no data | no data | Low downlink SNR | | 4966 | no data | no data | Low downlink SNR | | 4978 | no data | no data | Low downlink SNR | | 4981 | no data | no data | Low downlink SNR | | 4985 | no data | no data | Low downlink SNR | | 4986-5163 | no data | no data | Superior Conjunction | | 5164-5169 | no ar_rho | partial loss | Low downlink SNR | | 5173 | no ar_rho | partial loss | Low downlink SNR | | 5174 | no data | no data | No data | | 5175-5177 | no ar_rho | partial loss | Low downlink SNR | | 5178 | no data | no data | No data | | 5179-5180 | no ar_rho | partial loss | Low downlink SNR | | 5185-5187 | no ar_rho | partial loss | Low downlink SNR | | 5193-5195 | no data | no data | Low downlink SNR | | 5196-5198 | no ar_rho | partial loss | Low downlink SNR | | 5199-5202 | no data | no data | Low downlink SNR | | 5203 | no ar_rho | partial loss | Low downlink SNR | | 5206-5222 | no data | no data | Low downlink SNR | | 5223-5224 | no ar_rho | partial loss | Low downlink SNR | | 5225-5226 | no data | no data | Low downlink SNR | | 5227 | no ar_rho | partial loss | Low downlink SNR | | 5228-5229 | no data | no data | Low downlink SNR | | 5235-5247 | no data | no data | Low downlink SNR | | 5250-5634 | no data | no data | No mapping | | 5635-5660 | partial loss | invalid data | Radiometer saturation | | 5635 | no ar_rho | invalid data | Low downlink SNR | | 5637-5638 | no data | invalid data | Low downlink SNR | | 5641 | no ar_rho | invalid data | Low downlink SNR | | 5643 | no ar_rho | invalid data | Low downlink SNR | | 5645 | no data | invalid data | Low downlink SNR | | 5647-5648 | no ar_rho | invalid data | Low downlink SNR | | 5650 | no ar_rho | invalid data | Low downlink SNR | | 5651-5653 | no data | invalid data | Low downlink SNR | | 5654 | no ar_rho | invalid data | Low downlink SNR | | 5655-5660 | no data | invalid data | Low downlink SNR | | 5663 | no ar_rho | partial loss | Low downlink SNR | | 5664 | no data | no data | Low downlink SNR | | 5667 | no ar_rho | partial loss | Low downlink SNR | | 5668-5669 | no data | no data | Low downlink SNR | | 5671 | no ar_rho | partial loss | Low downlink SNR | | 5676 | no ar_rho | partial loss | Low downlink SNR | | 5679 | no ar_rho | partial loss | Low downlink SNR | | 5689 | no ar_rho | no data | Low downlink SNR | | 5691 | no ar_rho | no data | Low downlink SNR | | 5702 | no ar_rho | no data | Low downlink SNR | | 5711 | no data | no data | Low downlink SNR | | 5718 | no ar_rho | no data | Low downlink SNR | | 5726 | no data | no data | Low downlink SNR | | 5732 | no ar_rho | no data | Low downlink SNR | | 5735-5736 | no ar_rho | partial loss | Low downlink SNR | | 5738 | partial loss | no data | Low downlink SNR | | 5739-5740 | no ar_rho | no data | Low downlink SNR | | 5746 | no ar_rho | no data | Low downlink SNR | | 5748- | no data | no data | No mapping | +-------------+--------------+--------------+--------------------------+ Transmitter Failure All data on this disk are subject to the failure of downlink transmitter A that occurred on January 4, 1992 during the playback of orbit 3880, and the gradual failure of the backup transmitter B. See the notes for disk MG_2016 for further details. VV-polarization Test During orbits 4567-4574, while passing over Beta Regio, the spacecraft was rotated by 90 degrees about the axis of its high-gain antenna. This changed the polarization received by the SAR and radiometer modes from HH (E-field tangential to surface) to VV (E-field normal to surface) in order to study the effect that this would have on the observed radar backscatter cross-section and radio-thermal emissivity. A side-effect of the rotation is that no altimetry data were returned, since the al- timetry antenna no longer pointer toward the Venus surface. Gravity Mapping For one orbit per day beginning with orbit 4683, the high-gain antenna was pointed toward earth during periapsis passage in order to map the Venus gravity field. No radar data were taken on these orbits. High_Resolution Altimetry Test For three orbits, 4919-4921, as Magellan passed over the chasma region between Thetis Regio and Atla Regio, the high-gain antenna was pointed to the nadir and the SAR imager was operated as an altimeter. The results of this test, in which the cross-track footprint size is beam- limited to about 10 km and the along-track footprint size is frequency- limited to better than 50 meters, will be published elsewhere. Radiometer Saturation During orbits 5635 through 5660, S-band down-link telemetry was transmitted through the high-gain antenna during the mapping period. This caused the radiometer to saturate and no emissivity measurements were possible. Restricted Latitude Range Latitude coverage was less than nominal for all orbits on this disk. The chief reasons were (1) reduction of down-link telemetry bandwidth from 268 Kbaud to 115 Kbaud to compensate for the transmitter problems, and (2) need for the SAR antenna to turn away from Earth during data playback due to overheating at certain Earth-Sun-Venus geometries. The maximum range of latitude coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 4501 - 4985 42N 45S 42N 45S 42N 45S 42N 45S 5164 - 5249 1N 51S 0N 52S 1N 51S 0N 52S 5635 - 5747 16N 42S 16N 45S 16N 42S 16N 45S ----------------------------------------------------------- ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.03901-03960;1 | | | | ARCDR.03961-04020;1 | | | | ARCDR.04021-04080;1 | | | | ARCDR.04081-04140;1 | MGMORB FIT33 | | MG_2016 | ARCDR.04141-04200;1 | Jan 6, 1993 | | | ARCDR.04201-04260;1 | using orbits 376-5747 | | | ARCDR.04261-04320;1 | | | | ARCDR.04321-04380;1 | | | | ARCDR.04381-04440;1 | | | | ARCDR.04441-04500;1 | | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 3901-3953 | no data | no data | Downlink testing | | 3959 | no data | no data | Low downlink SNR | | 3960-3962 | no data | partial loss | Low downlink SNR | | 3963-3976 | no data | no data | Low downlink SNR | | 3977-4030 | no data | no data | Battery reconditioning | | 4032-4035 | no ar_rho | partial loss | Low downlink SNR | | 4054 | no data | no data | Low downlink SNR | | 4061 | no data | no data | Low downlink SNR | | 4070 | no ar_rho | partial loss | Low downlink SNR | | 4092 | no ar_rho | partial loss | Low downlink SNR | | 4121-4122 | no ar_rho | partial loss | Low downlink SNR | | 4128 | no ar_rho | partial loss | Low downlink SNR | | 4136 | no ar_rho | partial loss | Low downlink SNR | | 4142 | no data | no data | Low downlink SNR | | 4163-4164 | no data | no data | Low downlink SNR | | 4212 | no data | no data | Downlink testing | | 4224 | no ar_rho | partial loss | Low downlink SNR | | 4273 | no data | no data | Low downlink SNR | | 4312-4314 | no data | no data | Heavy rain at DSN | | 4315-4318 | no data | no data | Low downlink SNR | | 4329 | no ar_rho | partial loss | Low downlink SNR | | 4331 | no ar_rho | partial loss | Low downlink SNR | | 4333 | no data | no data | Low downlink SNR | | 4334 | no ar_rho | partial loss | Low downlink SNR | | 4336-4338 | no ar_rho | partial loss | Low downlink SNR | | 4339-4347 | no data | no data | Low downlink SNR | | 4348 | no ar_rho | partial loss | Low downlink SNR | | 4349 | no data | no data | Low downlink SNR | | 4351 | no ar_rho | partial loss | Low downlink SNR | | 4354 | no data | no data | Low downlink SNR | | 4356 | no data | no data | Low downlink SNR | | 4357-4358 | no ar_rho | partial loss | Low downlink SNR | | 4359 | no data | no data | Low downlink SNR | | 4360-4361 | no ar_rho | partial loss | Low downlink SNR | | 4362 | no data | no data | Low downlink SNR | | 4363 | no data | no data | Occultation gap | | 4364-4374 | no ar_rho | partial loss | Low downlink SNR | | 4376 | no ar_rho | partial loss | Low downlink SNR | | 4381-4382 | no ar_rho | partial loss | Low downlink SNR | | 4384-4385 | no data | no data | Low downlink SNR | | 4389-4390 | no data | no data | Downlink subcarrier off | | 4392 | no data | no data | Low downlink SNR | | 4396 | no ar_rho | partial loss | Low downlink SNR | | 4401-4402 | no ar_rho | partial loss | Low downlink SNR | | 4408 | no data | no data | Canberra tracking gap | | 4418 | no ar_rho | partial loss | Low downlink SNR | | 4423-4425 | no ar_rho | partial loss | Low downlink SNR | | 4445-4448 | no ar_rho | partial loss | Low downlink SNR | | 4451 | no data | no data | Low downlink SNR | | 4452-4455 | no ar_rho | partial loss | Low downlink SNR | | 4456-4458 | good data | good data | Cycle 1 DLAP (Hestia) | | 4459 | no ar_rho | partial loss | Low downlink SNR | | 4467 | no ar_rho | partial loss | Low downlink SNR | | 4470 | no ar_rho | partial loss | Low downlink SNR | | 4474 | no ar_rho | partial loss | Low downlink SNR | | 4475 | no data | no data | Low downlink SNR | | 4485 | no ar_rho | partial loss | Low downlink SNR | | 4488 | no ar_rho | partial loss | Low downlink SNR | | 4492-4493 | no data | no data | Heavy rain at DSN | | 4497-4500 | no ar_rho | partial loss | Low downlink SNR | +-------------+--------------+--------------+--------------------------+ Transmitter Failure All data on this disk are subject to the failure of downlink transmitter A that occurred on January 4, 1992 during the playback of orbit 3880. Telemetry was switched to the backup transmitter B, which was used for the remainder of the mapping mission. Transmitter B suffered from a gra- dual failure of its X-band modulator, which manifested itself as a spurious signal that often interfered with the downlink data side-band. Downlink Testing After orbit 3889, transmitter B was switched off for several days while the X-band modulator problem was diagnosed. Tests were made to determine the optimal operating temperature that would minimize the spurious modu- lation. Low Downlink SNR Data from many orbits were totally lost, and others partially lost, when the spurious modulation from transmitter B exceeded the capabilities of the Deep Space Network (DSN) receivers to lock onto the phase-modulated data side-band. This varied from day to day depending on the distance to the spacecraft, the state of the Earth's ionosphere, the local weather at the DSN station, and the gradual deterioration of the transmitter B modulator. No ar_rho (Reflectivity) Data To reduce the effect of the spurious modulation on altimetry processing, a digital filter was used whenever the symbol signal-to-noise ratio at the DSN dropped below a critical threshold. This filter preserved the accuracy of ranging measurements at the expense of introducing large inaccuracies in the computation of the surface power reflection coeffi- cient (field ar_rho in ar_rec records). Hestia Imaging Test During a three-orbit period (4456-4458), a special command load was exe- cuted to view an area in eastern Hestia Rupes in which there was some evidence of surface changes in images made during the first and second mapping cycles. Unfortunately, as a result of inaccurate navigation data, these three orbits did not target the region in question. Restricted Latitude Range Latitude coverage was less than nominal for all orbits on this disk. The chief reasons were (1) reduction of down-link telemetry bandwidth from 268 Kbaud to 115 Kbaud to compensate for the transmitter problems, and (2) need for the SAR antenna to turn away from Earth during data playback due to overheating at certain Earth-Sun-Venus geometries. The maximum range of latitude coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 3954 - 3958 26N 79S 16N 83S 26N 79S 16N 83S 4031 - 4131 77N 18S 76N 19N 77N 18S 76N 19N 4132 - 4234 18N 18S 18N 18S 18N 18S 18N 18S 4235 - 4367 77N 14N 76N 13N 77N 14N 76N 13N 4368 - 4500 42N 45S 42N 45S 42N 45S 42N 45S ----------------------------------------------------------- ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.03721-03780;1 | MGMORB FIT29 | | MG_2015 | ARCDR.03781-03840;1 | April 14, 1992 | | | ARCDR.03841-03900;1 | using orbits 1841-2100 | | | | and 3631-3889 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 3793 | partial loss | partial loss | Radiometer calibration | | 3801-3806 | no data | no data | DSN shutdown - Xmas | | 3807 | partial loss | partial loss | DSN shutdown - Xmas | | 3813 | partial loss | partial loss | DSN outage | | 3835 | partial loss | partial loss | DSN outage | | 3853 | partial loss | partial loss | DSN outage | | 3855 | partial loss | partial loss | DSN outage | | 3856-3858 | no data | no data | DSN shutdown - New Year | | 3880-3976 | partial loss | partial loss | Transmitter A failure | | 3881-3882 | no data | no data | Transmitter A failure | | 3884-3888 | no data | no data | Transmitter A failure | +-------------+--------------+--------------+--------------------------+ Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. The range of radiometric coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 3721 - 3770 4S 80S 4S 82S 4S 80S 4S 82S 3771 - 3881 7N 80S 7N 83S 7N 80S 7N 83S ----------------------------------------------------------- Transmitter A Failure The X-band modulator on telemetry transmitter A failed on January 4 1992 during the playback of orbit 3880. The task was transferred to the back- up transmitter which was known to have a problem with its modulator. Some partial data playbacks (orbits 3883 and 3889) were achieved before the end of Cycle II. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | | MGMORB FIT26 | | | ARCDR.03301-03360;1 | May 27, 1992 | | | | using orbits 1307-1661 | | | | and 3097-3450 | | +-----------------------+--------------------------------+ | | ARCDR.03361-03420;1 | MGMORB FIT27 | | MG_2014 | ARCDR.03421-03480;1 | June 4, 1992 | | | ARCDR.03481-03540;1 | using orbits 1481-1832 | | | | and 3271-3621 | | +-----------------------+--------------------------------+ | | ARCDR.03541-03600;1 | MGMORB FIT28 | | | ARCDR.03601-03660;1 | June 12, 1992 | | | ARCDR.03661-03720;1 | using orbits 1661-2011 | | | | and 3451-3800 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 3594-3667 | partial loss | partial loss | S/C roll | | 3716-3719 | no data | V-pol data | polarimetry test | +-------------+--------------+--------------+--------------------------+ Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. The range of radiometric coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 3301 - 3358 7N 80S 7N 85S 7N 80S 7N 85S 3359 - 3461 4S 89S 4S 85S 4S 89S 4S 85S 3462 - 3667 20S 74S 20S 74S 49S 89S 49S 85S 3668 - 3715 4S 80S 4S 82S 4S 80S 4S 82S 3716 - 3719 57N 65S - - 57N 65S - - 3720 - 3720 4S 80S 4S 82S - - - - ----------------------------------------------------------- In addition, during orbits 3594-3667, the spacecraft executed a 20 deg- ree roll about the HGA axis at the end of each mapping pass in order to shade the star tracker from sunlight. Polarimetry test For the duration of orbits 3716-3719 the spacecraft was rotated 90 deg- rees about the HGA boresight in order to perform a polarimetry test. There is no altimetry data for these orbits. Radiometry data is verti- cally polarized (E-vector parallel to the scattering plane). ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.03001-03060;1 | MGMORB FIT25 | | | ARCDR.03061-03120;1 | May 1, 1992 | | | ARCDR.03121-03180;1 | using orbits 1111-1482 | | | | and 2901-3271 | | MG_2013 +-----------------------+--------------------------------+ | | | MGMORB FIT26 | | | ARCDR.03181-03240;1 | May 27, 1992 | | | ARCDR.03241-03300;1 | using orbits 1307-1661 | | | | and 3097-3450 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 3030 | partial loss | partial loss | Premature end of data | | 3035-3037 | partial loss | partial loss | Premature end of data | | 3042-3044 | partial loss | partial loss | Premature end of data | | 3256 | no data | partial loss | S/C timing error | +-------------+--------------+--------------+--------------------------+ Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. The range of radiometric coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 3001 - 3101 6N 90S 6N 85S 6N 90S 6N 85S 3102 - 3204 2S 90S 2S 85S 2S 90S 2S 85S 3205 - 3255 5S 90S 5S 85S 5S 90S 5S 85S 3256 - 3300 7N 90S 7N 85S 7N 80S 7N 85S ----------------------------------------------------------- ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | | MGMORB FIT23 | | | ARCDR.02761-02820;1 | April 8, 1992 | | | | using orbits 787-1110 | | | | and 2465-2900 | | MG_2012 +-----------------------+--------------------------------+ | | ARCDR.02821-02880;1 | MGMORB FIT24 | | | ARCDR.02881-02940;1 | April 24, 1992 | | | ARCDR.02941-03000;1 | using orbits 946-1307 | | | | and 2731-3096 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 2852 | no data | good data | | | 2764-2768 | partial loss | partial loss | DSN bad weather | | 2879 | partial loss | partial loss | Radiometer calibration | | 2913-2923 | partial loss | partial loss | Premature S/C turn | | 2926-2936 | no data | variable pol | S/C rotation | | 2939-2976 | no data | variable pol | S/C rotation | +-------------+--------------+--------------+--------------------------+ Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. The range of radiometric coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 2761 - 2936 75N 67S 78N 66S 42N 90S 42N 85S 2937 - 2998 18S 90S 18S 85S 18S 90S 18S 85S 2999 - 3000 6N 90S 6N 85S 6N 90S 6N 85S ----------------------------------------------------------- Spacecraft Rotation Spacecraft over-heating had become so serious by orbit 2925 that it had to be rolled through 180 degrees during mapping in order to reduce the temperature of critical systems, especially the remaining data recorder. With the altimetry antenna pointing away from the planet, no altimetry data were taken. The corresponding radiometry data are taken with a con- tinually changing polarization angle. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.02161-02220;2 | | | | ARCDR.02221-02280;1 | MGMORB FIT22 | | | ARCDR.02281-02340;1 | April 9, 1992 | | | ARCDR.02341-02400;1 | using orbits 426-676 | | | ARCDR.02401-02460;1 | and 2216-2586 | | MG_2011 | ARCDR.02461-02520;2 | | | +-----------------------+--------------------------------+ | | ARCDR.02581-02640;2 | MGMORB FIT23 | | | ARCDR.02641-02700;1 | April 8, 1992 | | | ARCDR.02701-02760;1 | using orbits 787-1110 | | | | and 2465-2900 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 2176-2218 | good data | partial loss | Radiometer test | | 2270 | no data | no data | DSN problem - high wind | | 2649 | no data | no data | S/C anomaly | | 2650 | partial loss | partial loss | S/C anomaly | | 2656-2657 | partial loss | partial loss | DSN tracking problem | +-------------+--------------+--------------+--------------------------+ Radiometer Test The last minute of data taking during orbits 2176-2218 was devoted to a radiometer test. Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. The range of radiometric coverage is given by the following table: Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 2161 - 2218 89N 9N 85N 9N 89N 9N 85N 9N 2219 - 2365 44S 72S 44S 71S 68S 90S 67S 85S 2366 - 2464 37S 70S 36S 70S 65S 90S 65S 85S 2587 - 2642 20S 80S 19S 80S 41S 90S 40S 85S 2643 - 2688 14N 90S 14S 85S 14N 90S 14S 85S 2689 - 2716 75N 70S 78N 66S 42N 90S 42N 85S 2717 - 2760 75N 67S 78N 67S 41N 90S 42N 85S ----------------------------------------------------------- NOTE: orbits 2176-2218 and 2465-2586 were published on the MG_2010 volume. Although 2465-2586 strictly belong to Cycle II of Magellan map- ping, they fill the coverage gap caused by solar superior conjunction during Cycle I. ======================================================================== The following tables list the nominal coverage of all Cycle 1-2 orbits, LATITUDE COVERAGE OF CYCLE 1 ORBITS Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 376 - 403 90N 51S 85N 52S 69N 71S 69N 74S 404 - 558 90N 51S 85N 52S 55N 79S 54N 83S 559 - 661 90N 51S 85N 52S 69N 71S 69N 74S 662 - 676 90N 51S 85N 52S 55N 79S 54N 83S 787 - 1030 90N 51S 85N 51S 55N 79S 55N 78S 1031 - 1045 90N 16S 85N 17S 55N 58S 54N 60S 1046 - 1097 81N 19S 80N 19S 52N 51S 52N 52S 1098 - 1249 75N 42S 74N 43S 52N 62S 52N 64S 1250 - 1301 77N 40S 77N 41S 55N 61S 54N 62S 1302 - 1354 82N 40S 81N 41S 55N 65S 54N 67S 1355 - 1949 90N 51S 85N 52S 55N 79S 55N 83S 1950 - 2001 90N 42S 85N 42S 90N 42S 85N 42S 2002 - 2054 90N 34S 85N 35S 90N 34S 85N 35S 2055 - 2106 90N 14S 85N 14S 90N 14S 85N 14S 2107 - 2175 90N 9N 85N 9N 90N 9N 85N 9N 2176 - 2218 90N 9N 85N 9N 90N 9N 85N 9N ----------------------------------------------------------- LATITUDE COVERAGE OF CYCLE 2 ORBITS Orbit Even Orbits Odd Orbits Range Radiometer Altimeter Radiometer Altimeter ----------------------------------------------------------- 2219 - 2365 44S 72S 44S 71S 68S 90S 67S 85S 2366 - 2464 37S 70S 36S 70S 65S 90S 65S 85S 2587 - 2642 20S 80S 19S 80S 41S 90S 40S 85S 2643 - 2688 14N 90S 14S 85S 14N 90S 14S 85S 2689 - 2716 75N 70S 78N 66S 42N 90S 42N 85S 2717 - 2936 75N 67S 78N 67S 41N 90S 42N 85S 2937 - 2998 18S 90S 18S 85S 18S 90S 18S 85S 2999 - 3101 6N 90S 6N 85S 6N 90S 6N 85S 3102 - 3204 2S 90S 2S 85S 2S 90S 2S 85S 3205 - 3255 5S 90S 5S 85S 5S 90S 5S 85S 3256 - 3358 7N 90S 7N 85S 7N 80S 7N 85S 3359 - 3461 4S 90S 4S 85S 4S 90S 4S 85S 3462 - 3667 20S 74S 20S 74S 49S 90S 49S 85S 3668 - 3715 4S 80S 4S 82S 4S 80S 4S 82S 3716 - 3719 57N 65S - - 57N 65S - - 3720 - 3770 4S 80S 4S 82S 4S 80S 4S 82S 3771 - 3881 7N 80S 7N 83S 7N 80S 7N 83S ----------------------------------------------------------- ======================================================================== BUGS IN ARCDRLST PROGRAM The following problems have been noted in the software and documentation that were included in the [SOFTWARE] directories of the first 10 ARCDRCD volumes MG2001 through MG_2010, and have been corrected in the versions included on all subsequent ARCDR disks: [SOFTWARE]ARCDRLST.C [SOFTWARE]ARCDRLST.EXE [SOFTWARE]ARCDRLST.HQX Some output from the "echo" sub-command (ADF files only) was in- correct. When the first non-zero value of "tmpl" or "rstmpl" for a particular footprint occurred at a delay index "del" greater than 252, less than the correct number (i.e. 50) of non-zero values was reported. [SOFTWARE]ARCDRLST.C [SOFTWARE]ARCDRLST.EXE [SOFTWARE]ARCDRLST.HQX [SOFTWARE]ARCDRLST.TXT The brief description of RDF data type 26 ("Surface Brightness Tem- perature (K)" was erroneously reported as "Physical Surface Tempera- ture (K)", i.e. identical to data type 29. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.02041-02100;1 | MGMORB FIT20 | | | ARCDR.02101-02160;1 | October 15, 1991 | | | ARCDR.02161-02220;1 | using orbits 376-429 | | | | and 1951-2218 | | MG_2010 +-----------------------+--------------------------------+ | | ARCDR.02461-02520;1 | MGMORB FIT21 | | | ARCDR.02521-02580;1 | October 21, 1991 | | | ARCDR.02581-02640;1 | using orbits 587-676, | | | | 787-887, and 1951-2218 | +-------------+-----------------------+--------------------------------+ NOTE: orbits 2465-2586 are included on this disk since, although they strictly belong to Cycle II of Magellan mapping, they fill the coverage gap caused by solar superior conjunction during Cycle I. +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 2118 | partial loss | partial loss | AACS failure | | 2119-2127 | no data | no data | AACS failure | | 2128-2129 | partial loss | partial loss | AACS failure | | 2041-2218 | partial loss | partial loss | Premature S/C turn | | 2172-2175 | no data | no data | OTM burn | | 2176-2218 | partial loss | partial loss | Pointing Error | | 2219-2464 | no data | no data | Constant Incidence | | 2465-2586 | partial loss | partial loss | Premature S/C turn | | 2490-2518 | partial loss | no loss | SAR Range-Gate Error | | 2587-2640 | no data | no data | Constant Incidence | +-------------+--------------+--------------+--------------------------+ Orbit Overlap Orbits 2176-2218 overlap with orbits 376-429 from the first mapping cycle. Similarly, orbits 2576-2586 overlap with orbits 787-796 from the first mapping cycle. The two sets of radius values have been averaged when correcting for spacecraft tracking errors and when determining the physical surface temperature in RDF files. AACS failure Data was lost from periapsis on orbit 2118 until periapsis on orbit 2129. This was due to the fifth in a series of AACS computer failures to plague the Magellan spacecraft since Venus orbit insertion. Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. From orbits 2041-2054, altimetry and radiometry coverage ends at 35'S latitude, from orbits 2055-2106, coverage ends at 14.8'S, from orbits 2107-2158, coverage ends at 7.4'N, and from orbits 2159-2218, coverage ends at about 9'N. For orbits 2465-2519, altimetry and radiometry coverage extends from 51'N to 45.3'S latitude, and for orbits 2520-2586, it is from 52.7'N to 46.5'S. OTM Burn An orbit trim maneuver was performed on orbit 2172 to adjust the orbit period so that cycle 2 nadir tracks would precisely interleave with those of cycle 1. In this way, the altimeter can fully sample the planet from 85'N to 85'S. Pointing Error A spacecraft pointing error affected orbits 2176-2218 from 13.7'N to the end of mapping at 9'N. Within that latitude range, the data fields that are affected are all ar_rho reflectivity values in ADF files and some rr_emiss emissivity values in RDF files. Constant Incidence Mapping After orbit 2218, the Magellan high-gain antenna was pointed to the right side of the direction of motion during mapping. At the same time, the look-angle was varied so as to make all side-looking observations at nearly the same incidence angle, irrespective of latitude. This deviation from the nominal look-angle profile that was maintained during all of the first mapping cycle (orbits 376-2218) prevented correct altimetric reduction since the model echo templates that are matched against the data would be calculated for an incorrect geometry. The spacecraft returned to the left-looking nominal look-angle mode for orbits 2465-2586 in order to fill the Cycle I superior conjunction gap, and then returned to right-looking constant incidence-angle mapping. Altimetry data taken during constant incidence-angle mapping will be reduced and published at a later date. SAR Range-Gate Error Altimetry results from command upload 1110 are corrupted by an incorrect SAR range-gate setting that interfered with altimetry range determination. This only affects even-numbered orbits in the range 2489-2519 between 38.6'S and end-of-mapping at 45.3'S. also, see notes for MG_2001 and MG_2002. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.01861-01920;1 | MGMORB FIT19 | | MG_2009 | ARCDR.01921-01980;1 | October 7, 1991 | | | ARCDR.01981-02040;1 | using orbits 1771-2130 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 1950-2040 | partial loss | partial loss | Premature S/C turn | +-------------+--------------+--------------+--------------------------+ Premature Spacecraft Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping. From orbits 1950-2001, altimetry and radiometry coverage ends at 42.5S latitude. From orbits 2002-2040, coverage ends at 35.0S. Also, see notes for MG_2001 and MG_2002. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.01681-01740;1 | MGMORB FIT18 | | MG_2008 | ARCDR.01741-01800;1 | September 21, 1991 | | | ARCDR.01801-01860;1 | using orbits 1591-1955 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 1687-1697 | partial loss | partial loss | Poor X-band downlink | | 1692-1816 | low radii | good data | Poor ephemerides | +-------------+--------------+--------------+--------------------------+ Poor X-band downlink Several orbits produced degraded data due to problems with the spacecraft's X-band telemetry transmitter. This was swapped for a redundant unit on 03/14/91, and the problem went away. Poor Ephemerides Navigation solutions for orbits 1692-1816 are subject to systematic in- plane position errors of as much as 400 meters. The errors are worst for orbits 1743-1765 at latitudes between 52'N and 15'S, whose reported footprint radii (ar_rec fields ar_radius and ar_radius2) are consist- ently too low by 250-400 meters. Also, see notes for MG_2001 and MG_2002. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.01501-01560;1 | MGMORB FIT17 | | MG_2007 | ARCDR.01561-01620;1 | September 12, 1991 | | | ARCDR.01621-01680;1 | using orbits 1411-1770 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 1501-1607 | partial loss | partial loss | Premature S/C turn | | 1630 | partial loss | partial loss | AACS failure | | 1631-1633 | no data | no data | AACS failure | | 1634 | partial loss | partial loss | AACS failure | +-------------+--------------+--------------+--------------------------+ AACS failure Data was lost from periapsis on orbit 1631 until periapsis on orbit 1634. This was due to the fourth in a series of AACS computer failures to plague the Magellan spacecraft since Venus orbit insertion. The notes for MG_2001, MG_2002, and MG_2006 also apply to this disk. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.01321-01380;1 | MGMORB FIT16 | | MG_2006 | ARCDR.01381-01440;1 | August 20, 1991 | | | ARCDR.01441-01500;1 | using orbits 1231-1590 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 1321-1354 | partial loss | partial loss | Venus Occultation | | 1487-1500 | partial loss | partial loss | Premature S/C turn | +-------------+--------------+--------------+--------------------------+ Occultations When the spacecraft passes behind Venus (as seen from the Earth) during data play-back time, less than the full quantity of recorded data can be sent to Earth. This occurred for orbits 1321-1354, and restricted altimetry data to the latitude range from 81.1N to 67.3S, and radiometry from 82.3N to 65.5S. Premature Turns To reduce the risk of overheating several spacecraft systems, the SAR antenna was turned away from the planet before the end of mapping for delayed swaths starting with orbit 1487. Altimetry coverage ends at 64.5S latitude, and reflectivity measurements beyond footprint 886 (latitude 62.3S) have been flagged as bad. The equivalent cut-off in radiometry occurs at 58.3S. The notes for MG_2001 and MG_2002 also apply to this disk. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.01141-01200;2 | MGMORB FIT15 | | MG_2005 | ARCDR.01201-01260;2 | August 5, 1991 | | | ARCDR.01261-01320;2 | using orbits 1051-1416 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 1141-1320 | partial loss | partial loss | Venus occultation | | 1250 | partial loss | partial loss | Uplink command error | | 1315-1319 | good data | partial loss | Sun reflections | +-------------+--------------+--------------+--------------------------+ Radiometer Data Files (RDF): (a) Orbits 1315-1319 show the Sun reflected in the Venus surface at latitude 3S, resulting in emissivity values, rr_emiss, greater than unity. The notes for MG_2001 and MG_2002 also apply to this disk. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.00961-01020;2 | MGMORB FIT14 | | MG_2004 | ARCDR.01021-01080;2 | July 28, 1991 | | | ARCDR.01081-01140;2 | using orbits 871-1234 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 0961-1097 | partial loss | partial loss | DTR-A failure | | 0969 | partial loss | partial loss | Radiometer calibration | +-------------+--------------+--------------+--------------------------+ The notes for MG_2001 and MG_2002 also apply to this disk. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.00781-00840;3 | MGMORB FIT13 | | MG_2003 | ARCDR.00841-00900;3 | July 25, 1991 | | | ARCDR.00901-00960;3 | using orbits 787-1143 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 0781-0786 | no data | no data | Superior conjunction | | 0787-0960 | partial loss | partial loss | DTR-A failure | | 0814 | no data | no data | DSN outage | | 0815 | partial loss | partial loss | DSN outage | | 0825-0826 | no data | no data | Spacecraft anomaly | | 0827-0828 | good data | partial loss | Bad antenna pointing | | 0888-0891 | no data | no data | Uplink anomaly | | 0942 | partial loss | partial loss | Bad antenna pointing | | 0943-0945 | no data | no data | No downlink | +-------------+--------------+--------------+--------------------------+ The notes for MG_2002 also apply to this disk. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.00541-00600;4 | MGMORB FIT12 | | MG_2002 | ARCDR.00601-00660;4 | July 8, 1991 | | | ARCDR.00661-00720;4 | using orbits 376-676 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 0590-0661 | partial loss | partial loss | DTR-A failure | | 0677-0720 | no data | no data | Superior conjunction | +-------------+--------------+--------------+--------------------------+ Altimeter Data Files (ADF): (a) Data recorder A (DTR-A) degraded progressively from orbit 590 through orbit 1097, after which it was no longer used. During this period, much altimetric and radiometric data was lost. This results in missing footprints and degraded signal strength for those that remaining. Reflectivity measurements (ar_rho) are worse affected than planetary radius (ar_radius) and RMS meter-scale slope (ar_slope). The worst region spans footprints -200 through 735 of orbits 627 through 661. (b) Bands of anomalous RMS slope (ar_slope) and reflectivity (ar_rho) at latitudes of 9S and 23S are caused by an altimeter mode change con- fused by missing data (due to the data recorder failure). (c) The west face of Maxwell Montes rises almost 10 kilometers within a few altimeter footprints. The altimeter itself has an inherent range ambiguity of 10.02 kilometers, which makes it impossible to locate the west face from the altimeter echoes alone. The radius values in two regions (0.5E, 64.8N and 2.0E, 63.1N in orbits 578 through 583) have therefore been adjusted with the help of side-looking images of Maxwell from Magellan and Arecibo, adding or subtracting 10.02 km from each ar_radius value, but the assignment is tentative. The ambiguity will remain unless and until Magellan views that part of Maxwell at a different incidence angle. Radiometer Data Files (RDF): (d) The progressive failure of DTR-A from orbit 590 through 1097 results in many missing radiometer footprints. The notes for MG_2001 also apply to this disk. ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.00361-00420;4 | MGMORB FIT12 | | MG_2001 | ARCDR.00421-00480;4 | July 8, 1991 | | | ARCDR.00481-00540;4 | using orbits 376-676 | +-------------+-----------------------+--------------------------------+ +-------------+--------------+--------------+--------------------------+ | Orbit Range | Altimetry | Radiometry | Comments | +-------------+--------------+--------------+--------------------------+ | 0361-0375 | no data | no data | Prior to mapping | | 0452-0455 | partial loss | no data | Radar test number 5 | | 0490-0491 | partial loss | partial loss | Madrid DSN outage | +-------------+--------------+--------------+--------------------------+ The data format corresponds to the MIT Software Interface Specification document MIT-MGN-ARCDR v2.3 (Magellan Project document SCI002). The following notes and restrictions apply: Ephemeris Files (EPF): (a) These files are copied directly from the ALT-EDR data tapes, and may therefore inherit errors from them. Their format may NOT correspond precisely either to the NAIF Ephemeris SIS (NAV-135) or to the examples given in MIT-MGN-ARCDR v2.3. In particular, some lines are terminated by too many, or too few, carriage returns and/or line feeds. Altimeter Data Files (ADF): (b) Bad data records have NOT been eliminated from these files. The user should ALWAYS inspect the ar_flag fields and ignore records for which flags such as AR_BAD have been set. (c) All radii in ADF files have been corrected by the mgmorb processing phase, in which radii from crossing and near-crossing orbits are compared and in-plane ephemeris corrections computed. (d) Power reflection coefficient values (ar_rho) show a gradual increase at high latitudes. Since the surface emissivity (rr_emiss in RDF files) shows no corresponding drop in polar regions, the increase in the average value of ar_rho is probably an artifact of the data reduction process. (e) The signal quality index field (ar_sqi) is recorded in IEEE-754 single-precision floating-point format, not in the VAX format used for the other 4-byte floating-point fields. Radiometer Data Files (RDF): (f) The side-looking backscatter cross-section measurements reported in the rr_sar[0] and rr_sar[1] fields are derived from the block- adaptive-quantizer (BAQ) signal levels reported in radar burst headers, not from averaged C-BIDR image swaths as described in the MIT software design document, MIT-MGN-SDD v2.1. (g) There is a systematic bias to all radiometer data that depends on the time elapsed since start of mapping and on the behavior of the altimeter and, possibly, other on-board systems. The magnitude is of the order of 5K in system temperature, or a factor of 0.01 in emissivity. The bias is seen to change with command upload number and all RDF files have been re-processed through a data filter in an attempt to correct the problem. The filter has itself introduced subtle artifacts in the radiometer data (sudden jumps in data value at specific latitudes of the same magnitude as the original bias), but the overall systematic error is greatly reduced. ======================================================================== A data processing error has been discovered that affects all ARCDR products sent to DMAT prior to July 1991. Frequency components from separate altimeter bursts were incorrectly summed together, leading to a blurring of altimetry data in the along-track direction. The following products are affected: ARCDR.00146-00147;1 ARCDR.00541-00600;2 ARCDR.00901-00960;1 ARCDR.00361-00420;1 ARCDR.00541-00600;3 ARCDR.00901-00960;2 ARCDR.00361-00420;2 ARCDR.00601-00660;2 ARCDR.00961-01020;1 ARCDR.00361-00420;3 ARCDR.00601-00660;3 ARCDR.01021-01080;1 ARCDR.00421-00480;1 ARCDR.00661-00720;2 ARCDR.01081-01140;1 ARCDR.00421-00480;2 ARCDR.00661-00720;3 ARCDR.01141-01200;1 ARCDR.00421-00480;3 ARCDR.00781-00840;1 ARCDR.01201-01260;1 ARCDR.00481-00540;1 ARCDR.00781-00840;2 ARCDR.01261-01320;1 ARCDR.00481-00540;2 ARCDR.00841-00900;1 ARCDR.00481-00540;3 ARCDR.00841-00900;2 A formatting error has been discovered that affects all ARCDR products sent to DMAT prior to May 1991. The error occurs in all Radiometry Data Files (RDF), and concerns the length of the first aggregate SFDU in each file. This length, recorded in bytes 13-20 of the first physical record, was 00000358. The correct value is 00000454, and the RDF files should therefore begin with the ASCII string "CCSD1Z00000100000454". New versions of these products, without the formatting error, have been delivered to DMAT. Note that the mgmdqe analysis program and the read_arcdr() subroutine distributed on ARCDR CD-ROMs will successfully read both original and corrected RDF files. The following products are affected: ARCDR.00361-00420;1 ARCDR.00481-00540;1 ARCDR.00661-00720;2 ARCDR.00361-00420;2 ARCDR.00481-00540;2 ARCDR.00781-00840;1 ARCDR.00421-00480;1 ARCDR.00541-00600;2 ARCDR.00841-00900;1 ARCDR.00421-00480;2 ARCDR.00601-00660;2 ARCDR.00901-00960;1 ======================================================================== +-------------+-----------------------+--------------------------------+ | VOLUME_ID | PRODUCT_IDs | EPHEMERIS CORRECTION | +-------------+-----------------------+--------------------------------+ | | ARCDR.00361-00420;1 | MGMORB FIT4 | | MG_TEST3 | ARCDR.00421-00480;1 | November 18, 1990 | | | ARCDR.00481-00540;1 | using orbits 376-676 | +-------------+-----------------------+--------------------------------+ The data format corresponds to the MIT Software Interface Specification document MIT-MGN-ARCDR v2.1 (Magellan Project document SCI002). The following notes and restrictions apply: Orbit Header Files (OHF): (a) The SFDU keyword section refers to the processing of altimetry data files, not to radiometry data. (b) There are no RDF files for the 4 orbits comprising Radar Test 5 (452-455). The oh_nrad fields are therefore zero for these orbits. Ephemeris Files (EPF): (c) These files are copied directly from the ALT-EDR data tapes, and may therefore inherit errors from them. Their format may NOT correspond precisely either to the NAIF Ephemeris SIS (NAV-135) or to the examples given in MIT-MGN-ARCDR v2.1. In particular, some lines are terminated by too many, or too few, carriage returns and/or line feeds. (d) All radii in ADF files have been corrected by the mgmorb processing phase, in which radii from crossing and near-crossing orbits are compared and in-plane ephemeris corrections computed. The data in these products were processed by FIT4 of mgmorb on 1990-11- 18T13:06:29. Altimeter Data Files (ADF): (e) Bad data records have NOT been eliminated from these files. The user should ALWAYS inspect the ar_flag fields and ignore records for which flags such as AR_BAD have been set. (f) Because of the lack of C-BIDR data (see below), the power reflection coefficients in the ADF files have NOT been corrected for the diffuse scattering component. Therefore no AR_RHOC flag is set in any ar_flag fields, and the corresponding ar_rhocor fields contain zeroes. (g) The template fitting algorithm used to compute the surface power reflection coefficient, ar_rho, doesn't correctly account for echo profiles with multiple peaks. Values of ar_rho over rugged terrain should not be relied upon. A correction for this phenomenon will be introduced in subsequent versions of the ARCDR. (h) A systematic wave-like fluctuation in altimeter range values has been observed in the ADF data covering a wide area of the planet between 325E and 357E longitude, and 45N and 52N latitude. The amplitude is approximately 50 meters and the wavelength 100 km. Its cause is currently unknown, but it is likely to be an instrumental effect or data processing error. Radiometer Data Files (RDF): (i) No radiometry data is available for the 4 orbits comprising Radar Test 5 (orbits 452-455). The corresponding RDF files are null, i.e. the ARCDR tape contains an ANSI header (HDR) file, followed by two consecutive file marks, followed by an ANSI trailer (EOF) file, followed by a file mark. Software used to copy this tape (ARCDR.00421-00480;1) must treat this double file mark as a null file, NOT as the physical end of tape. (j) Only 26 C-BIDR orbits (376-399 and 403-405) were available when these ARCDR tapes were produced. RDF files generated from C-BIDRs are given version number 1. The remaining RDF files came from ALT- EDR products and bear the version number T1. These latter are all marked with the RR_NOS1 and RR_NOS2 flags in their rr_flag fields and they contain zeroes in their rr_sar and rr_sfoot arrays. (k) The average planetary radius at the footprint location, rr_radius, is derived from the Magellan topography model 4.0, NOT from Magellan altimeter data. Therefore, the RR_RADC flag is NOT set in the rr_flag field, and the surface emission temperature, rr_surftemp, and the emissivity, rr_emiss, have NOT been corrected accordingly. (l) There is a systematic bias to all radiometer data that depends on the time elapsed since start of mapping and on the behavior of the altimeter and, possibly, other on-board systems. The magnitude is of the order of 5K in system temperature, or a factor of 0.01 in emissivity. The bias is seen to change with upload number and all RDF files have been re-processed through a data filter in an attempt to correct the problem. The filter has itself introduced subtle artifacts in the radiometer data, sudden jumps in data value at specific latitudes, of the same magnitude as the original bias, but the overall systematic error is greatly reduced. ========================================================================