DESCRIPTION = "This file describes the format of the TABLE in the GVANF.TAB file. See the GVANF.LBL file for the full PDS label." OBJECT = COLUMN NAME = RECLEN /* unused */ DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 1 BYTES = 2 DESCRIPTION = "This field will removed in the final product. It is unused in this version." END_OBJECT = COLUMN OBJECT = COLUMN NAME = SAMPLE_COUNT DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 3 BYTES = 2 DESCRIPTION = "The total number of SCVDR ANF altimeter footprints used to compute the estimates of radar scattering properties given in this row of the table. The quantities given in later columns pertain only these footprints. Any altimeter footprint that is partially or completely contained inside this pixel is included. The distance from pixel center to footprint center is used to weight the averaging process. The extent of the altimeter footprint is defined by the first-order range-aliasing and frequency-aliasing points, or the antenna pattern's 3 dB beamwidth, whichever is smaller. Note that this is much larger than the definition used for the ARCDRCD ADF files, and near the poles results in each footprint overlapping hundreds of GVDR pixels." END_OBJECT = COLUMN OBJECT = COLUMN NAME = SCATTERING_ANGLE_COUNT DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 5 BYTES = 1 VALID_MINIMUM = 0 VALID_MAXIMUM = 10 DESCRIPTION = "The number of scattering angles for which estimates of scattering cross-section are given below in the object CROSS_SECTION_CONTAINER. The maximum scattering angle is limited by geometric factors, and decreases toward the poles. Only the first SCATTERING_ANGLE_COUNT angles are valid." END_OBJECT = COLUMN OBJECT = COLUMN NAME = SCATTERING_FIT_COUNT DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 6 BYTES = 1 VALID_MINIMUM = 0 VALID_MAXIMUM = 5 DESCRIPTION = "The number of analytic scattering models which have been fitted to the observed scattering law. Only the first SCATTERING_FIT_COUNT fits in SCATTERING_LAW_FITS_CONTAINER are valid." END_OBJECT = COLUMN OBJECT = COLUMN NAME = DOPPLER_CENTROID DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 7 BYTES = 2 OFFSET = -6000 SCALING_FACTOR = 0.183122 UNIT = HZ VALID_MINIMUM = -6000 VALID_MAXIMUM = 6000 DESCRIPTION = "The average observed centroid of the received altimetry echo spectrum." END_OBJECT = COLUMN OBJECT = COLUMN NAME = NADIR_TRACK_AZIMUTH_ANGLE DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 9 BYTES = 1 OFFSET = 0 SCALING_FACTOR = 1.44 UNIT = DEGREE VALID_MINIMUM = 0 VALID_MAXIMUM = 360 DESCRIPTION = "The average azimuthal angle of the spacecraft nadir track. The nadir point is the point on the surface intersected by the line between the spacecraft and the center of the planet. The nadir track is the locus of that point as it moves along the surface. The surface is assumed to be perfectly spherical for the purposes of calculating the azimuthal angle. The azimuthal angle is defined in two ways, depending on the image map projection in use. For the Sinusoidal and Mercator map projections, the direction of the nadir track is expressed as a heading on a compass, in degrees clockwise from North. For example, if the nadir point is moving due east, the azimuthal angle is defined to be 90 degrees. Since this definition becomes useless near the poles, this field is set to zero above 85 degrees of latitude for the Sinusoidal projection. The Mercator projection does not extend to such high latitudes. For the Polar Stereographic map projection, the azimuth angle is expressed in the cartesian map coordinates rather than in geographic coordinates. This makes the azimuth angle more useful for interpretation because its meaning no longer varies with position. First, the azimuth direction is computed as above. Then, this direction is transformed to a direction in map coordinates; the transformed vector is parallel to the vector originating at the nadir point and pointing in the azimuth direction. This vector is expressed in degrees clockwise from the +Y (up) direction on the map. For example, if the north polar projection has 0 degrees of longitude at the bottom, then a footprint at 90 degrees of longitude with a true azimuth of 90 degrees (nadir point moving due east) has a transformed azimuth of 0 degrees. The nadir point appears to be moving in the +Y direction on the map. The relationship between true azimuth and transformed azimuth is simple. For the north polar projection with 0 degrees longitude at the bottom, CARTESIAN_AZIMUTH = GEOGRAPHIC_AZIMUTH - LONGITUDE and for the south polar projection with 0 degrees longitude at the top, CARTESIAN_AZIMUTH = GEOGRAPHIC_AZIMUTH + LONGITUDE As discussed in the GVHDR.LBL file, the group of altimetry observations used in this row forms a 'cohort'. Within a cohort, the azimuth angle of each observation falls within a single interval of size 360/N, where N is the value of ANF_COHORT_AZIMUTH_COUNT from the GVHDR file. We can reconstruct that interval by noting that the average azimuth angle of all the observations (given in this column) falls within the same interval. Specifically, we find a value of I that satisfies I * 360.0 / N <= AZIMUTH_ANGLE < (I+1) * 360.0 / N where N = ANF_COHORT_AZIMUTH_COUNT I = integer between 0 and N-1 inclusive The azimuth angles of all observations in the cohort lie in the interval [I*360 , (I+1)*360), and their average value is given in this column." END_OBJECT = COLUMN OBJECT = COLUMN NAME = PAD DATA_TYPE = "N/A" START_BYTE = 10 BYTES = 1 DESCRIPTION = "This field will be removed in the final data product ad AZIMUTH_ANGLE will be increased to two bytes." END_OBJECT = COLUMN OBJECT = CONTAINER NAME = CROSS_SECTION_CONTAINER START_BYTE = 11 BYTES = 10 REPETITIONS = 10 DESCRIPTION = "A vector of specific radar cross section measurements, indexed by incidence angle. Only the first SCATTERING_ANGLE_COUNT elements of this vector are valid. The values were obtained by linear inversion of a discretized integral equation for scattering from a sphere." OBJECT = COLUMN NAME = SPECIFIC_RADAR_CROSS_SECTION DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 1 BYTES = 1 OFFSET = -3 SCALING_FACTOR = 0.024 UNIT = "N/A" /* see DESCRIPTION */ VALID_MINIMUM = 0.001 VALID_MAXIMUM = 1000 SAMPLING_PARAMETER_NAME = INCIDENCE_ANGLE SAMPLING_PARAMETER_UNIT = DEGREE SAMPLING_PARAMETER_INTERVAL = 0.5 MINIMUM_SAMPLING_PARAMETER = 0.25 MAXIMUM_SAMPLING_PARAMETER = 4.75 DESCRIPTION = "The observed specific radar cross-section at a given angle of incidence. The units of this measurement are dimensionless, meters-squared per meters-squared, and are recorded here logarithmically. To obtain the actual cross-section, apply the scaling and offset given above and raise 10 to this power." END_OBJECT = COLUMN END_OBJECT = CONTAINER OBJECT = CONTAINER NAME = CROSS_SECTION_VARIANCE_CONTAINER START_BYTE = 21 BYTES = 10 REPETITIONS = 10 DESCRIPTION = "A vector of the formal variance of the above specific radar cross section measurements, indexed by incidence angle. Only the first SCATTERING_ANGLE_COUNT elements of this vector are valid. The values were obtained by linear propagation of errors, based on physical estimates for the thermal and speckle noise in the received radio signal." OBJECT = COLUMN NAME = SPECIFIC_RADAR_CROSS_SECTION_VARIANCE DATA_TYPE = MSB_UNSIGNED_INTEGER START_BYTE = 1 BYTES = 1 OFFSET = -3 SCALING_FACTOR = 0.032 UNIT = "N/A" /* see DESCRIPTION */ VALID_MINIMUM = 0.001 VALID_MAXIMUM = 100000 SAMPLING_PARAMETER_NAME = INCIDENCE_ANGLE SAMPLING_PARAMETER_UNIT = DEGREE SAMPLING_PARAMETER_INTERVAL = 0.5 MINIMUM_SAMPLING_PARAMETER = 0.25 MAXIMUM_SAMPLING_PARAMETER = 4.75 DESCRIPTION = "The formal variance of the corresponding entry in the object SPECIFIC_RADAR_CROSS_SECTION. The units of this value are dimensionless, meters-fourth per meters-fourth, and are recorded here logarithmically. To obtain the actual variance, raise 10 to the value given here." END_OBJECT = COLUMN END_OBJECT = CONTAINER OBJECT = CONTAINER NAME = SCATTERING_LAW_FITS_CONTAINER START_BYTE = 31 BYTES = 50 REPETITIONS = 5 DESCRIPTION = "A collection of best fit scattering models to the observed scattering law in SPECIFIC_RADAR_CROSS_SECTION. The fits are made using the formal variance in the object SPECIFIC_RADAR_CROSS_SECTION_VARIANCE. Each repetition contains the results of a single least-squares fit of the empirical scattering function to a particular scattering model." ^STRUCTURE = "GVNFF.FMT" END_OBJECT = CONTAINER