N.B.: This data set is saved for historical purposes only; it is not considered to be of archival quality.  The 'raw data' mentioned in this description are saved as PDS data set PHB2-M-TS-2-THERM/VIS-IMGEDR-V1.0  Data Set Overview : The first part of this description repeats general information from the raw data description and the latter part refers specifically to this data set. See the raw data set template for more description of the raw data.  In February and March, 1989, the Termoskan instrument on board the Phobos '88 spacecraft of the USSR acquired a limited set of very high resolution simultaneous observations of the reflected solar flux (hereafter referred to as the visible channel) and emitted thermal flux (thermal infrared (IR)) from Mars's equatorial region. These are, so far, the highest spatial resolution thermal data ever obtained for Mars. Four slightly overlapping thermal panoramas (also called scans or swaths) cover a large portion of the equatorial region from 30S to 6N latitude. Simultaneous visible panoramas were taken during each of the four observing sessions; due to spacecraft memory limitations, visible channel processing was stopped early relative to the thermal channel for 2 of the sessions (2 and 4). Thus, the visible channel panoramas are shorter than the thermal panoramas for these sessions.  The instrument was fixed to the spacecraft with the optical axis pointing in the anti-solar direction. As a consequence, all observations are at approximately zero degrees phase angle and only daytime observations were acquired. Scan lines were acquired approximately going from North to South on the planet at a rate of 1 line per second.  In the first session (taken Feb 11, 1989), the periapse altitude of the spacecraft's elliptical orbit was 1150 km and the resolution at nadir was approximately 300 m per pixel. The thermal and visible channel panoramas from this session exhibit longitudinal gaps of varying size between scan lines. Within each scan line (acquired in the North-South direction), however, full resolution and coverage were maintained. In the remaining three sessions (one taken on March 1, 1989 and two on March 26, 1989), the panoramas were acquired from a circular orbit of altitude 6300 km with a resolution at nadir of approximately 1.8 km per pixel. In these panoramas, line and frame scanning correspond; therefore, there are not significant gaps between scan lines and geometrical distortions primarily occur only because of the sphericity of the planet. The dark West-East bands in observing sessions 3 and 4 are from the shadow of Phobos.\n Each image consists of 384 samples. The number of lines varies depending upon how long the instrument was on in any given panorama. The data is 8 bit data with dn values ranging from 0 to 255 for both the thermal and the visible channels. West is towards the top of each image file and North is to the right.  There are three major differences between this data set and the raw data set First, the raw data has been stripped of all non- image samples, leaving 384 samples. Second, all panorama fragments of the raw data files have been recombined so that each of the full length edited files (designated by file names ending with ed) contain one entire panorama (either thermal or visible). Thus, there are 8 full length files corresponding to the 4 Termoskan observing sessions. For ease of display on some systems, each of these full length files has also been chopped into 512 line fragments (with file names ending in f# where # is the fragment number for that panorama). Note that the last fragment file of each panorama may have less than 512 lines depending upon the length of the full length file. Third, data from the visible and thermal channels have been aligned so that a given line and sample in a thermal image should correspond to the same location on Mars as the same line and sample in the corresponding visible channel image.  Various actions were required to align the thermal and visible data files. Three factors affected the alignment of lines between the thermal and visible files. First, there were offsets at the beginning of files, probably caused by data lines added on Earth. This initial offset was determined by comparison of surface features near the beginnings of the panoramas. Then, non-data lines were removed from the beginning of the appropriate file. Second, there are dropped (missing) data lines in some of the thermal data and in some of the visible data. In most of the raw data, no extra lines were added to fill these gaps. Comparison of the same surface features in both visible and thermal raw images on either side of the dropped lines was used to determine the number of lines missing. This number of black (dn : 0) lines were inserted to represent the missing lines in the edited files. There were rare occurrences of seemingly superfluous dn : 0 lines in the raw data. These lines were removed. Within the raw data set there are also occasional lines with dn : (a constant value not equal to zero). Most of these lines appeared to preserve geometry, so were left in the edited files.  There was also a constant offset between thermal and visible samples (North-South direction). The offset ranged from 2 to 3 samples but appeared to be constant for any given observing session. This offset was corrected for in the edited data by adding either 2 or 3 dn : 0 samples to the beginning of each line in the thermal channel.  All thermal files within the edited data set have 388 samples per line, with either 2 or 3 leading dn : 0 samples, 384 data samples, and either 1 or 2 trailing dn : 0 samples. All visible channel files have 384 samples per line.  The UT start and stop times given in the full length edited file labels are times at the spacecraft, not earth receive times.  PDS1 Data Set Parameters : SAMPLING_PARAMETER_NAME : PIXEL SAMPLING_PARAMETER_RESOLUTION : 1 MINIMUM_SAMPLING_PARAMETER : N/A MAXIMUM_SAMPLING_PARAMETER : 384 SAMPLING_PARAMETER_INTERVAL : 1 MINIMUM_AVAILABLE_SAMPLING_INT : N/A SAMPLING_PARAMETER_UNIT : N/A DATA_SET_PARAMETER_NAME : DN NOISE_LEVEL : UNK DATA_SET_PARAMETER_UNIT : DIMENSIONLESS

Confidence Level Overview : The alignment of thermal and visible edited files should be good to within approximately +/- 1 pixel.  Lengths of the scans derived from the start and stop times and the 1 line per second scan rate do not always agree with the lengths of the scans, probably due primarily to lines added or subtracted at the beginnings and ends of the 'original' (raw) files. However, the magnitude of the difference in all cases is less than 5 minutes (300) lines and thus an insignificant error for most applications.  In addition, the following confidence notes remain from the raw data: noise in every eighth sample of the thermal channel amounting to a positive 1 or 2 dn increase (probably tied somehow into the calibration that was going on at a similar rate); sporadic single pixel spikes that occur occasionally within the data; occasional partial lines which appear corrupted; occasional whole lines with single dn values that appear to preserve geometry, but have no value as data; depending upon the panorama either the first or last of the 384 sample pixels is corrupted in the thermal channel, leaving at most 383 good samples per line; and two bright West-East lines (affecting the same samples in each line) in visible panorama 1 (possibly caused by reflections off the spacecraft?). The thermal channel appears to be very well calibrated to at least 3 K (Murray, et al. 1991).