PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "Known errors and/or anomalies in the volumes" PUBLICATION_DATE = 2018-02-28 END_OBJECT = TEXT END ERRORS AND/OR ANOMALIES IN THE CURRENT VOLUME Volume CORADR_0195, Version 03 ------------------------------ 1. The Cassini Radar Transition file (EXTRAS/CRT_195_V03.TAB) contains no information about ScanStart and ScanEnd transitions. 2. The uncompressed LBDR and BIDR products have attached labels. Normally, a file that has been compressed with ZIP would have been generated without an attached label. 3. In the volume index table (INDEX/INDEX.TAB), double quotes enclose all the date/time values. Normally, PDS date/time values are not quoted, but quoting makes parsing easier for some applications. 4. The HTML documents in the DOCUMENT directory contain HTML character codes that, while all-ASCII, are not easily interpretable by someone who is reading the HTML documents as text documents. For example, "α" represents the lower-case Greek character "alpha" and is rendered as such in a web browser. Equivalent and more legible character codes (e.g., "&#alpha;") are available as of the HTML 4.0 specification but cannot be used here, as PDS requires HTML documents to comply to the HTML 3.2 specification. 5. Antenna temperature, brightness temperature, and receiver temperature are defined in Janssen, M. A., "An Introduction to the Passive Microwave Remote Sensing of Atmospheres," Chapter 1 in Atmospheric Remote Sensing by Microwave Radiometry, (M. Janssen, ed.), pp. 1-35, Wiley & Sons, New York (1993). The archived value in the SBDR and LBDR files gives uncalibrated antenna temperature in units of Kelvin. The best current algorithm for correcting the archived antenna temperatures is Ta_corrected = Ta_archive * ( 0.920 - 0.0041*( t - 1.90 ) ) where t = time in years and fractional years since 2004.0 (0 UTC on 1 Jan 2004) This algorithm is based on the radioastronomical flux scale at 2-cm wavelength by direct comparison of distant (unresolved) Titan measurements by the Cassini radiometer with VLA measurements of Titan reported by Butler and Gurwell, 2004. This algorithm will improve with time as more distant Titan measurements are obtained and as more radioastronomical comparison sources are included. Butler, B. J., Gurwell, M. A. 2004. Radio Wavelength Observations of Titan with the VLA. Bull. Am. Astron. Soc. 36, 6.04. This algorithm applies also to all preceeding volumes. 6. Ideally the calibrated antenna temperature is referenced to cold sky at 2.7 K, although no guarantee is made that this zero-level accounting has been correctly made. Also, the antenna temperature is defined for this application as just the average brightness temperature in the measured beam out to 2 degrees from the beam axis, and does not allow for possible contributions from the far sidelobes (sidelobes outside of 2 degreees). The archived value will include an additional contribution if the far sidelobes happen to fall on other than cold sky. In particular, there is an offset to be expected and accounted for when an extended source like Titan or Saturn is observed from a close distance. A more detailed explanation will be found in Janssen et al., 2009. System gain is the quantity that multiplies the raw sky counts to convert to the uncalibrated Kelvin scale. Receiver_temp is the receiver noise temperature Tr (comparison made at internal reference switch). The receiver temperature plus the antenna temperature is equal to the total signal (raw counts times system gain). 7. ant_temp_std is a measure of the rms uncertainty of Ta, and is only an estimation. It is obtained as the standard deviation of Ta for three points, Ta(I-1), Ta(I), and Ta(I+1), and is a useful measure that identifies questionable data. For example, it gets large when the beam is sweeping across a brightness discontinuity. 8. All BIDRs except for the byte-valued backscatter images (BIB*.IMG) were produced by JPL. The byte-valued backscatter images were produced by USGS. The USGS BIDRs have unit strings in their labels which are all CAPS. The other BIDRs have lower case units. According to the PDS dictionary, both are acceptable. 9. Checksums were not computed for floating point valued BIDRs. The CHECKSUM keyword was assigned a zero value. 10. In the primary BIDR images a technique was used to remove systematic errors due to thermal noise and BAQ compression during downlink. The technique appears to have a slight negative bias for very low SNR, i.e. when the signal power is less than one tenth the thermal noise power. Without noise subtraction, backscatter values are artificially high and always positive. With noise subtraction, negative values occur both due to the aforementioned bias and due to residual random error. Byte-valued BIDRs are produced by transforming all data to Decibels by taking the logarithm and then multiplying by 10. Data is clipped below a minimum value (typically -20 dB) determined by the OFFSET keyword in the attached label. All negative backscatter values or value belows 0.01 (-20 dB)are assigned to the minimum pixel value. Anyone interested in viewing data below this threshold needs to use the REAL-VALUED backplanes. 11.The submitted volume CORADR_0143 has an erroneous INDEX and CUMINDEX entry for BIFQE10N073_D143_I049S01_V02. 12.Every volume from CORADR_0144 to CORADR_0229 has missing CUMINDEX entries for Iapetus_049_3. 13. There are some invalid resistive load counts at the very beginning which result in incorrect antenna temperatures. 14. Volumes CORADR_0265 and CORADR_0266 have missing CUMINDEX entries for COARDR_0035_V03. 15. Even though radiometry measurements were made using all 5 beams during regular SAR segments, only beam 3 brightness temperature results are archived due to calibration challenges of the other four beams. 16. Because the LBDR product was longer than 2 GB, the product has been split into two files. The filenames and product ID's have an extra three characters (_P1 or _P2) to denote part 1 and part 2. This does not conform to the SIS. 17. The rot_velocity_target_y field is incorrectly assigned in all Cassini RADAR SDBR, ABDR, and LBDR products, but the angular velocity vector of the spacecraft can be computed independently from the time series of the 3 spacecraft body frame axes, sc_X_target, sc_Y_target, and sc_Z_target. 18. The Beammask and Number of Looks BIDR backplanes have a value for SAMPLE_TYPE="UNSIGNED INTEGER" instead of "UNSIGNED_INTEGER". This field needs to be fixed by the user before being ingested by ISIS software. 19. The AAREADME file that is included as part of each PDS volume has a section addressing the version number of all the data products. The AAREADME file for flybys TA-T30 had erroneously reported that the volumes with PRODUCT_VERSION_ID 02 for flybys T36-T77 represent products processed with the non-synchronous pole, instead of reporting as being processed by the synchronous pole. This comment is corrected in the AAREADME files in later flybys. 20. The burst numbers in the ABDR SUMMARY file for this flyby are local rather than global. The global burst number is the local burst number plus the Data Take Number times 1,000,000. ERRORS AND/OR ANOMALIES IN PREVIOUS VOLUMES 1. The last field of a few records in the ABDR SUMMARY file corresponding to Flyby T8 have unusually large numbers. These erroneous values will not be fixed. Instead the user can exclude these data points while using results from the ABDR SUMMARY file.