Data Set Overview : This data set contains products acquired by the UVI instrument of the Venus Climate Orbiter (VCO, also known as PLANET-C and AKATSUKI) spacecraft. This data set uses the Committee on Data Management and Computation (CODMAC) data level numbering system. The UVI CDRs are considered Level 3 or Composite Data (equivalent to NASA Level 1B). The CDRs are reconstructed from Level 2 or Edited Data. This data set consists entirely of FITS files. Calibrated images in units of radiance are included. The headers of the FITS files are included as part of the data set, and much of the FITS header information is reproduced in the PDS labels. Processing : Overview -------- The data processings are done on DANS (Data Analysis Network System) managed by C-SODA (Center for Science-satellite Operation and Data Archive), ISAS/JAXA at Sagamihara, Kanagawa, Japan. Note that DANS consists of SIRIUS (Scientific Information Retrieval and Integrated Utilization System), EDISON (Engineering Database for ISAS Spacecraft Operation Needs), ``Reformatter'', DARTS (Data ARchives and Transmission System) and data analysis servers. The summary of the data processing is as follows. The data downlinked as telemetry are transferred to the data accumulation system at ISAS, and are registered to SIRIUS and are sorted in time. From SIRIUS, level 0 data are retrieved to the Reformatter for the PLANET-C Project Team that is provided by C-SODA to each mission. All processings (data pipeline) after level 0 until level 3 are done on the Reformatter. These procedures are executed automatically. To implement these procedures, various program codes are used, written in C, C++, Fortran 90/95, Ruby, Python, Perl, and POSIX shell. Definitions of the processing levels ------------------------------------ The definitions of the processing levels for UVI, IR1, IR2, and LIR instruments are same for simplicity and homogeneity. The processing levels are defined as follows: abbr name description ---- -------- --------------------------------------------------- L0 Level 0 raw data files from telemetry. L1a Level 1a counts in FITS format. L1b Level 1b flipped and rotated L1a with summary of geometry information in FITS format. L2b Level 2b calibrated physical quantity in FITS format. L2c Level 2c (more) calibrated physical quantity in FITS format. L3b Level 3b L2b mapped onto longitude-latitude grids in NetCDF format that is preprocessed using the limb-fitting technique for correction of pointing of the camera. L3c Level 3c L2c mapped onto longitude-latitude grids in NetCDF format that is preprocessed using the limb-fitting technique for correction of pointing of the camera. Detailed description of the processings --------------------------------------- This section describes detailed procedure at each processing level. The summarized diagram of the pipeline is shown below: (1) (2) (3) (4) (5) SIRIUS -----> L0 -----> L1a -----> L1b -----> L2b -----> L3b \ \(4) (5) `-> L2c -----> L3c (1) L0 data processing L0 data are consists of three kinds of file, tile of image, common ancillary data for the image and instrument-specific ancillary data for the image. The image size of each tile file is 128 x 128 pixels. These L0 data are retrieved from the SIRIUS. The tile files of image are usually compressed by HIREW algorithm, so the tile files are decompressed at the first step. The decompressed tile files are converted from unsigned 16-bit integer into signed 16-bit integer, and then concatenating decompressed tile files, the raw image file is created. If one or more tile files are missing, missing value is substituted to the corresponding pixels at this processing level. For LIR images, only valid region of data is cropped after concatenation of tile files. If the compressed tile file is identified as corrupted, e.g., the data size of the tile file is not equal to the data size recorded in the header of the tile file, only pixels supposed to be valid are decoded and invalid pixels are filled with missing value. (2) L1a data processing From the raw image and ancillary data files in L0, L1a FITS file is created. If there are wrong ancillary data, the corrected data are stored in the header of the HDU of L1a FITS file using other source. This is currently applied only to UVI images. Some types of the ancillary data to be stored in the header of the HDU of L1a FITS file, e.g., value of P_OBSPRG that represents observation program ID used to acquire image, are automatically determined by command history files or data files created from HK (House Keeping) telemetry packets. Note that the command history files stores the commands sent from the ground to the spacecraft, and it can be retrieved from EDISON. The data files created from HK telemetry packets also can be retrieved from EDISON. For IR1 and IR2 images, command sequences (i.e., observation program) to acquire image are changed from the planned one at the instrument design phase to reduce the total time for taking images as short as possible. This change caused the issue that cannot uniquely determine both of selected filter and exposure time for each image only from the telemetry data. This issue is solved by a script using the executed observation programs extracted from command history files and the relationship between executed observation program used for taking each image and known behavior of the instrument-specific ancillary data that depends on the executed observation program. (3) L1b data processing From L1a FITS file, L1b FITS file and associated geometry information FITS file are created using SPICE kernels and the SPICE toolkit. The orientation of image data become nominal (spacecraft +Y axis is upward with the coordinate described in 'document/imagecoord.txt') at this processing by the procedure combining vertical flipping of the image and some of the 90-degree rotations. This procedure differs depending on the instruments/channels. What kind of operation has been done is recorded as value of the P_FLPROT keyword in the header of the HDU in FITS file. This operations are nominally done as follows: cam channels operations P_FLPROT --- -------- -------------------- -------- UVI all rotate CCW 270 deg 3 IR1 all flip vertically 10 IR2 1.65 um no rotation/flipping 0 IR2 others rotate 180 deg 2 LIR all flip vertically 10 For the purpose of quick look, JPEG image is created for each FITS image file. (4) L2b and L2c data processing From L1b FITS file, L2b and L2c FITS file are created using FITS files for calibration, depending on the instrument and the channels. L2c is ``more calibrated'' version than L2b. This processing level is available for IR1 and LIR at now. For IR1, handling of pixels with special flag values during smear correction are different between L2b and L2c. For L2b product, if the pixels with special flag values appear in the column in a quadrant, all the values of the pixels at the column in the quadrant are set to missing value. IR1 L2b product is processed with the aim of photometric analysis. For L2c product, if the pixels with special flag values appear in the column in a quadrant, contribution from the pixels to the total amount of smear is estimated using available value near the pixel in the same column. IR1 L2c product is processed with the aim of cloud tracking. For LIR, in addition to L2b data calibration process, L2c data processing applies calibration using baffle (hood) temperature. This requires baffle (hood) temperature acquired from HK, so the product is not available when HK lacks. For the purpose of quick look, JPEG image is created for each FITS image file also at this processing level. (5) L3b and L3c data processing From L2b or L2c FITS file, L3b or L3c NetCDF file, and L3bx or L3cx NetCDF file are created using SPICE kernels and SPICE toolkits. The fully-automated algorithms of limb-detection, limb-fitting and interpolation onto equally spaced longitude-latitude grids has been implemented for the processing. For verification of the result of limb-detection and limb-fitting, L3bx or L3cx NetCDF file is also created. This file also contains correction of pointing of the camera. Using the correction of pointing of camera, L3bx or L3cx FITS file is created. L3bx and L3cx FITS files have a similar structure to geometry information file (``geo'' file), so one can use L3bx or L3cx FITS file as pointing- corrected geometry information file instead of geometry information file created at the L1b data processing. Assumption on the altitude for observed quantity ------------------------------------------------ For geometry calculations, what altitude that the observed quantity is coming from and includes information on is roughly assumed as follows: cam channels assumed altitude --- ------------- ---------------- UVI 283 nm 70 km 365 nm 70 km IR1 0.90 um day 60 km 0.90 um night 60 km 0.97 um 60 km 1.01 um 60 km IR2 1.735 um 50 km 2.26 um 50 km 2.32 um 50 km 2.02 um 70 km 1.65 um N/A LIR pic 65 km The assumed altitude is recorded in the FITS header keyword, S_CLDALT. Parameters : The primary data is ADU (analog-digital unit) counts that are nominally proportional to the number of photons received at the detector (CCD) with the applied filter. The ADU counts are nominally proportional to radiance at the target wavelength corresponds to the applied filter. The radiance data at the target wavelength corresponds to the filter are derived from ADU counts, the flat data, and the coefficients to convert from ADU counts to the radiance value. In this data set, radiance data are provided. If the image is acquired with ``TOP_OB'' mode, pixel values in the ``TOP_OB'' area are set to the missing pixel flag value because pixel values in the ``TOP_OB'' area are not meaningful in this processing level. For the filters used in the UVI instrument, see ``catalog/uviinst.cat'' for details. Data : Overview -------- There is only one kind of image data FITS file. Each value in data array represents value at the center of the pixel. For the definition of the image coordinate and relationship with indexes of data array, please refer the ``document/imagecoord.txt'' file. The image data FITS file has ``_l1b_'', ``_l2b_'', or ``_l2c_'' in the filename depending on the processing level of the file. File format and structure ------------------------- The files with the extension ``.fit'' under ``data'' directory are FITS format file. These FITS files are considered to be compliant with the FITS Standard Version 4.0 published online on 22 July 2016 by the IAUFWG except for handling of keywords that stores numeric value. If value of the keyword is supposed to be ``Not Available'', the value is set to 'N/A' in string literal in spite of definition of the keyword that stores numeric value. This is a work around for non-existence of numeric literals that represent special values in FITS Standard Version 4.0. For each image file, image data is stored in the data part of the secondary HDU (Header Data Unit) as IMAGE extension. The list of HDU in the geometry files is as follows: HDU 0: Primary HDU (header only) HDU 1: Image data File naming conventions ----------------------- The file naming conventions for the data files are same over the four cameras, UVI, IR1, IR2, and LIR. In addition to the four cameras, the data of LAC and RS have very similar file naming conventions. In this section, the file naming conventions for the four cameras are described. The filename has the format {cam}_{YYYY}{MM}{DD}_{hh}{mm}{ss}_{filter}_{level}_v{ver}.{ext} where {cam}: abbreviated name of cameras, i.e., uvi, ir1, ir2, and lir Note that for LAC and RS data, lac and rs are used, respectively. {YYYY}: year in four-digits {MM}: month in two-digits {DD}: day in two-digits {hh}: hour in two-digits {mm}: minute in two-digits {ss}: second in two-digits Note that {YYYY}-{MM}-{DD}T{hh}:{mm}:{ss} means the representative time of observation for the image in UTC. This time is also stored in HDU of the FITS file as string value of DATE-OBS keyword. {filter}: abbreviated filter name or type of image with 3 characters used to acquire image For each camera, values of {filter} and corresponding NAIF name of channel are listed below. {cam} {filter} NAIF name of channel used to acquire image ----- -------- ------------------------------------------ uvi 283 VCO_UVI_283 or VCO_UVI_283_TOPOB dif VCO_UVI_DIF or VCO_UVI_DIF_TOPOB 365 VCO_UVI_365 or VCO_UVI_365_TOPOB sht VCO_UVI_SHT or VCO_UVI_SHT_TOPOB ir1 09d VCO_IR1_09D 09n VCO_IR1_09N 097 VCO_IR1_097 101 VCO_IR1_101 dif VCO_IR1_DIF drk VCO_IR1_DRK ir2 174 VCO_IR2_174 226 VCO_IR2_226 232 VCO_IR2_232 202 VCO_IR2_202 165 VCO_IR2_165 drk VCO_IR2_DRK lir pic VCO_LIR_PIC opn VCO_LIR_OPN sht VCO_LIR_SHT {level}: abbreviated name of product The values of {level} is summarized in the following table. Note that the l3{b,c} and l3{b,c}x products are not provided as part of PDS3 data set, but will be provided at DARTS at ISAS/JAXA and PDS ``annex''. {level} corresponding DATA_SET_ID description -------- ------------------------- --------------------------- l1b VCO-V-{CAM}-2-EDR-V{VER} uncalibrated count data l2{b,c} VCO-V-{CAM}-3-CDR-V{VER} calibrated data with physical dimension geo VCO-V-{CAM}-3-SEDR-V{VER} geometry data at the center of each pixel l3{b,c} not applicable interpolated data projected onto longitude-latitude l3{b,c}x not applicable grid data for evaluation of automated limb-fitting and pointing corrected data that can be used instead of ``geo'' {ver}: version string of the product in 2 digits The value is larger than or equal to 10. When the version number appeared in DATA_SET_ID is multiplied by 10, the result is equal to the value of {ver}. {ext}: extension of the file The following typical extensions are included in this data set except for ``nc'' that is only included in l3{b,c} and l3{b,c}x products. The ``data'' directory contains only ``fit'' and ``lbl'' files, and the ``browse'' directory contains only ``jpg'', ``html'', and ``lbl'' files. {ext} description ----- ---------------------------------------- fit FITS file based on the FITS Standard 4.0 lbl PDS3 label file jpg JPEG file html HTML (mostly compliant with HTML 5.2) nc NetCDF file in NetCDF-4 Format Structure and size of image data -------------------------------- All UVI images consist of a multiple of tiles. One tile represents subimage with 128 x 128 pixels. Almost all tiles are compressed by the lossless data compression algorithm, HIREW. Each compressed tile is uncompressed to obtain raw tile data, and then raw image data that consists of multiple tiles is reconstructed by concatenating raw tile data files. Then the data is stored in FITS file with ancillary data. Therefore the data has 128*m pixels in horizontal and 128*n pixels in vertical, where m, n are integer and are within [1, 8]. Special pixels and its expressions in data array ------------------------------------------------ The following three types of special pixels are defined. terminology description --------------- ------------------------------------------------- missing pixel Data of the pixel is missing in the telemetry due to loss of the packets or the override by other data in the DR (Data Recorder). dead pixel Detector element of the pixel is damaged permanently by some reason, e.g., hit of X-rays to the corresponding detector element. saturated pixel Data at the pixel that are out of range from the nominal measurement due to receiving too much photons to the detector element. The following special values are defined and are recorded in the header of the HDU in FITS file. keyword description ------- ------------------------------------------------------ P_MPIXV Missing pixel flag value. Data at missing pixels are substituted this value. P_DPIXV Dead pixel flag value. Data at dead pixels are substituted this value. If dead pixels are not known, the value of the pixel will be 'N/A'. P_SPIXV Saturated pixel flag value. Data at saturated pixels are substituted this value. If saturated pixels are not identified at this processing level or are expressed using value of the keyword P_SPIXO, the value of the pixel will be 'N/A'. P_SPIXO Saturated pixel offset value. Data at saturated pixels are added this offset value to the original value of each pixel. If saturated pixels are not identified at this processing level or are expressed using value of the keyword P_SPIXV, the value of the pixel will be 'N/A'. This keyword is only used for IR2 L2b data. For verbosity, the following keywords are also used to record number of special pixels in the data in the header of the HDU. keyword description ------- ---------------------------------------------- P_MPIXN Number of missing pixels in the stored data. P_DPIXN Number of dead pixels in the stored data. P_SPIXN Number of saturated pixels in the stored data. Parameters used for calibration ------------------------------- The conversion method from counts into physical quantity, filenames, and parameters used to convert counts into physical quantity and/or used for calibration are recorded in the FITS header keywords as follows: keyword description -------- ------------------------------------ UV_FLAT filename of flat-field image UV_C2F method for converting counts to flux UV_C2FK1 value K1 appeared in UV_C2F UV_C2FK0 value K0 appeared in UV_C2F EXPOSURE exposure time in seconds See also ``document/uvical.txt'' for the details. Ancillary Data : +Y-axis Inversion Events ------------------------ In order to ensure thermal stability of the spacecraft and its instruments, the spacecraft +Y-axis must be inverted relative to the solar system plane periodically. The dates of these inversions are as follows: Date Events ------------------- -------------- 2015-12-09T23:36:00 south to north 2016-02-08T23:16:00 north to south 2016-11-24T05:00:00 south to north 2017-02-01T04:30:00 north to south 2017-11-16T01:00:00 south to north 2018-02-23T03:00:00 north to south 2018-04-04T05:41:00 south to north 2018-10-04T04:00:00 north to south Geometry information -------------------- The data on geometry in FITS header were calculated using the VCO SPICE kernels data set, VCO-V-SPICE-6-V1.0. This data set is available at DARTS in ISAS/JAXA and the PDS SPICE Archives in JPL/NASA. Detailed geometry information associated with images in this data set is provided in VCO-V-UVI-3-SEDR for purpose of reference. Coordinate System : In Space -------- Some geometric quantities appearing in the labels and the header of FITS files are in J2000 coordinates. In this coordinate, the +Z-axis points northward along the Earth's J2000 rotation axis and the +X-axis points toward the first point of aries. On Venus -------- For Venusian geometry, IAU VENUS that is defined as the planetocentric coordinate system for Venus is used. For Image --------- For all the data stored in the IMAGE extension HDU in FITS files provided in this data set, +Y-axis of the spacecraft is upward and -Z-axis of the spacecraft is rightward, when we use the commonly-used coordinate system with the origin at the lower-left corner of the image, horizontal axis (or X-axis or 1st axis) oriented from left to right, vertical axis (or Y-axis or 2nd axis) oriented from bottom to top. This coordinate system is commonly used in visualization software of FITS file, such as SAOImage DS9. The file ``document/imagecoord.txt'' describes detailed descriptions on the relationships between the image coordinate and indexes of the data used in this data set. Software : No software is included in this data set. However, the data products, being FITS files, can be readily accessed by means of a variety of FITS readers. PLANET-C Project Team members have been successful in using SAOImage DS9 version 7.6 by Smithsonian Astrophysical Observatory, the astropy module for Python version 3.0.3 (Python 3.7 has been used successfully), and the IDL Astronomy Users' Library. Note that for some of these readers, the existence of multiple HDU in the file must be included in the issued command.

Confidence Level Overview : See [YAMAZAKIETAL2018] for a description of the calibration applied to this data set. Review : Prior to release, this data set will be reviewed by the UVI team and the PDS Atmospheres Node. Data Coverage and Quality : Data Coverage ------------- The periods without observations and the reasons are as follows: Period Reason ------------------------ ------------------------------------------- 2010-05-22 -- 2010-12-07 Cruise phase and 1st trial of VOI 2010-12-11 -- 2015-12-06 Sun orbiting phase 2015-12-15 -- 2016-01-14 Initial checkout 2016-02-10 -- 2016-02-22 Not nominal attitude by misoperation 2016-05-26 -- 2016-06-14 Superior-conjunction 2017-12-28 -- 2018-01-18 Superior-conjunction Quality ------- Each image may contain salvaged area. The salvaged area is created by decompression of corrupted tile data. Even if the tile data is corrupted, some of the pixels still have uncorrupted value due to the characteristics of the data compression algorithm, HIREW. By diagnostic message of the decompression command or by human inspection, some pixel values in the uncompressed corrupted tile data are identified as wrong values and are filled with the missing value recorded in P_MPIXV keyword, and some of the pixels are left as is. This keyword and P_SALVn keywords indicate all of the salvaged areas included in the image data and warn users that these areas may contain wrong values. The following keywords for ``salvaged area'' are defined and are recorded in the header of the HDU in FITS file. keyword description ------- --------------------------------------------------------- P_NSALV number of salvaged areas. P_SALVn x- and y-ranges of salvaged area. The format of the string is '[x0,x1]x[y0,y1]' where x0, x1, y0 and y1 are positive integers. The salvaged area is within [x0,x1] in x-axis and [y0,y1] in y-axis, in the image coordinate (if the ROI function is used, the image coordinate differs from the full-size image coordinate). This salvaged area corresponds to one corrupted, salvaged tile data and the ranges of the area are recorded in each P_SALVn keyword. The ``n'' in the keyword used here is a non-negative integer that ranges from 0 to P_NSALV-1. The filter wheel that is driven by the stepper motor occasionally does not stop at the commanded position exactly but stops at near the commanded position. This results in a partially obstructed image. If the obstruction is off disk, the effect is minimal. If the obstruction is on-disk, then partial images of the planet can result, including identification of obstructed areas as having legitimate geometry information. The images with the affected pixels in this manner are identified with value of UV_FPFLG in the FITS header. The value of this header keyword does not ensure that there are affected pixels or not. There are circular, brighter or darker regions in UVI 283-nm image, e.g., around (295,185) -- (425,318), (162,11) -- (296,148), and (397,958) -- (432,988) in the full-size image coordinate. The first one is sometimes very clear and the others are relatively unclear. These regions seems to be fixed to the 283-nm filter used for acquiring image, so it will slightly move if the filter wheel's position is not nominal. In addition, there are non-circular brighter or darker regions. These brighter or darker regions are interpreted as stain or dig of the 283-nm filter by the UVI team. There are slantwise, linear brighter-darker pattern from upper-left to lower-right in the all image area. This pattern is interpreted as CCD device fixed pattern. These patterns are almost removed by subtraction of the dark image on the onboard image processing and/or by using the flat field image, but sometimes remains clearly even if it was calibrated. Anomalous count values are observed at several pixels from the edges of the detector area. For several lines at the right edge (vertical lines around x:1024 in the full-size image coordinate) and the top edge (horizontal lines around y:1024 in the full-size image coordinate), the count values usually tend to be smaller than expected. For lines at the left edge (vertical lines around x:1 in the full-size image coordinate), the count values usually tend to be larger than expected. One of the possible cause of the ``smaller case'' may be the mask nominally covering outside of the photosensitive area of the detector. The mask may cover the pixels at the edges of the photosensitive area, so the incoming light may be blocked by the mask, then the count values of the pixels at these edges may decrease. Therefore the signal at the pixels around the edges may not indicate correct value not only in the L1b data but also in the L2b data. The values in these area at L2b data are not specially treated, so they are still unreliable. The flat field pattern was also obtained as Venus images taken by using the diffuser in the orbit around Venus. The diffuser images of Venus are used to create the calibration flat pattern for the data processing on the ground. The UVI image data are corrected by the flat pattern and did not have the clear nonuniformity caused from the sensitivity difference of CCD detector pixel by pixel. However, the flat pattern is not a perfect correction for photometric analysis which requires careful treatment of the brightness. It is because the brightness gradient of one image due to vignetting slightly remains. Therefore the factor (a flat conversion factor), which is based on the pixel sensitivity estimated from the calibration results using the integrating sphere before the launch, is also prepared in ``calib/'' directory. It is recommended that the image is used basically for morphology analysis and image applied the flat conversion factors are used for photometric studies. The product of the conversion factors and the data for morphology analysis serves as the absolutely-calibrated brightness for photometric analysis. Note that the each flat conversion factor file is already rotated 270 degrees CCW, so you just need to operate data pixel by pixel. Please note that if the size of the image is not the full-size, please crop appropriate region of the flat data before multiplication. The UVI images acquired by the observation program ID 0x0a_v3 (limb observation) have not been applied smear correction onboard nor on the ground. Note that the observation program ID used to acquire image is recorded in value of P_OBSPRG keyword in the FITS header of the IMAGE extension HDU and in value of VCO:OBSERVATION_PROGRAM_ID in the associated PDS label in upper case. Limitations : There are no known limitations at now.