Dataset Overview : This volume contains Magellan C-BIDR (Compressed Resolution Basic Image Data Record) archive products. It also contains documentation files which describe the C-BIDRs. Each C-BIDR data directory contains the compressed image swaths obtained from one orbit and the ancillary files necessary to understand the data. The C-BIDR products archived on this volume are the exact products released by the Magellan Project, with additional PDS labels, swath index files, and documentation added for the convenience of the user. Supporting documentation and label files conform to the Planetary Data System (PDS) Standards, Version 3.0, Jet Propulsion Laboratory (JPL) document JPL D-7669.  Compressed resolution basic image data files consist of SAR image data acquired along one orbit. Pixel widths are 225m. Data are presented as 8 bit pixel brightness values where the brightness is in proportion to the radar scaled backscatter cross section. Scaling is accomplished by dividing the radar cross section value for each pixel by the value estimated from the Muhleman Law for the relevant incidence angle, converting the ratio to decibels, and scaling to a 1 to 251 output range. The 1 value corresponds to -20 dB and 251 to +30 dB, with a linear quantization of 0.2 dB in between. Data have at least 4 looks. Specifically, the scaled radar backscatter cross section is generated by:  1. Dividing the radar cross section by the value obtained from the Muhleman Law, alpha * cos(i) sigma[0] : --------------------------- (sin(i) + beta * cos(i))**3  where i : incidence angle, and alpha and beta are 0.0118 and 0.111, respectively [PETTENGILLETAL1988].  (Note: A value of 0.0188 was intended for the multiplicative alpha, but 0.0118 was used by mistake. Also, the incidence angles used to compute the Muhleman Law are systematically low by 0.5 degrees.)  2. Converting to dB by taking 10 times log base 10 of the ratio generated in the first step.  3. Scaling output to a byte DN value using the expression:  DN : 1 + ROUND({MIN [MAX(RV,-20), 30] + 20} * 5)  where RV : value produced in step 2, and ROUND : round to nearest integer.  C-BIDRs are presented as image files containing two integers at the beginning of each line. The first integer specifies the pixel offset t the first valid pixel; the second specifies the pixel offset to the las valid pixel. The remainder of the line consists of scaled backscatter cross section values.  Regions within 89 degrees of the equator have C-BIDRs in sinusoidal equal area projection; C-BIDR data located more than 80 degrees from th equator are also in oblique sinusoidal equal area projections. For the sinusoidal equal area projection, the origin is at 0 degrees latitude and the central meridian is the sub-spacecraft longitude at the equator adjusted to the nearest multiple of 225m, relative to a pixel centered 0 degrees longitude. For details of use of the oblique sinusoidal equa area projection see Magellan Software Interface Specification (SIS) Document, Full Resolution Basic Image Data Record, SDPS-101 [LEUNG1993]  The first mapping cycle C-BIDRs extend from the north pole to approximately 60 degrees south latitude for northern strips and from just below the north pole to about 70 degrees south latitude for intervening F-BIDR strips. Images sizes are approximately 120 samples b 70,000 lines.  Each C-BIDR orbit is located in a separate subdirectory on this CD-WO. Each product consists of 1 or 2 image files and 12 or 13 ancillary file for a total of 13 or 15 files. The higher numbers refer to orbits that include either north or south polar mapping. In addition, 1 or 2 index files have been added to assist in the use of the product.  Originally, up to 5 orbits of C-BIDR products were located, together with a number of other, ancillary files, on one 6250 BPI 2400 foot 9 track tape.  Each C-BIDR orbit consists of approximately 12 million bytes of image d and 13 million bytes of ancillary data. Included in the ancillary file are processing parameters, orbital information, and radar operational information.

Confidence Level Overview : Consult the ERRATA.TXT file in the root directory and ERR.TXT files in the data directories for information about errors that were detected during PDS label generation.