urn:nasa:pds:magellan_gvdr:data_gvdr:gvrdf_north 1.0 1.23.0.0 Product_Observational Magellan Mission urn:nasa:pds:context:investigation:mission.magellan data_to_investigation The Magellan Spacecraft Host urn:nasa:pds:context:instrument_host:spacecraft.mgn is_instrument_host Magellan Spacecraft Radar System Instrument urn:nasa:pds:context:instrument:mgn.rdrs is_instrument Venus Planet urn:nasa:pds:context:target:planet.venus data_to_target GVDR 376 4367 Stanford Center for Radar Astronomy gvdr_0001 Table cartography_parameters_to_image_object 0.00 360.00 90.00 60.00 Polar Stereographic 0 90 Coordinate Pair 18.225 18.225 5.79478 5.79478 -3253.1625 3253.1625 Planetocentric 6051.0 6051.0 6051.0 Positive East urn:nasa:pds:magellan_gvdr:document:gvdrsis data_to_document urn:nasa:pds:magellan_arcdr::1.0 data_to_derived_source_product gvrdf.tab 1994-05-10T22:45:17.000 Table 0 233947 The GVRDF file contains measures of the surface's thermal radiative efficiency derived from the side-looking microwave radiometer. (The RDF acronym stands for 'Radiometry Data File', one of the data files in the ARCDR data product. Within the software documentation, the acronym EDF, or 'Emissivity Data File', from the SCVDR data product, may also be used because of its similarity to the RDF.) This file is a table; each row in the table summarizes RDF results in a particular radiometry viewing geometry. The location and number of rows associated with each pixel are given by the corresponding values of 'RDF Start' and 'RDF Samples' in GVPIDX.TAB. See the descriptions in the GVTIDX.XML and GVPIDX.XML files for the overall organization of the GVDR. These files describe the division of the planet into pixels and organization of pixels into rectangular tiles. 6 0 10 Sample Count 1 1 UnsignedMSB2 2 The total number of radiometer footprints used to compute the estimates of thermal emission properties given in this row of the table. The quantities given in later columns pertain only these footprints. Any radiometry footprint that is partially or completely contained inside this pixel is included. Each footprint is derived from a single record in the ARCDR RDF file. The footprints used in this row share a common observational geometry, given explicitly by the columns 'Azimuth Angle', 'Incidence Angle', and 'Polarization Angle', and implicitly by the pixel address. This pixel may have entries in other rows, and if so at least one of the three angles will be different from this row. Azimuth Angle 2 3 UnsignedMSB2 2 degree 0.00549367 The average azimuthal angle of the radiometry observations. The azimuthal angle is defined in two ways, depending on the image map projection in use. For the Sinusoidal and Mercator map projections, it is defined as the local azimuth direction toward the spacecraft when viewed by an observer at the boresight intercept point on the planet surface, in degrees clockwise from North. For example, if the spacecraft appears to be due east of the observer, the azimuth angle is 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 framelet 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 framelet at 90 degrees of longitude with a true azimuth of 90 degrees (spacecraft to the east) has a transformed azimuth of 0 degrees. The vector from the framelet to the spacecraft appears to point 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 radiometry 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 'RDF 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 less than or = 'Azimuth Angle' less than (I+1) * 360.0 / N where N = 'RDF 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. Incidence Angle 3 5 UnsignedMSB2 2 degree 0.00137342 The average emission angle of the radiometry observations. This is the angle between the local mean surface normal and the direction of the emitted radiation on its way to the spacecraft. Normal emission is thus 0 degrees, and grazing emission is 90 degrees. This quantity is obtained directly from the ARCDR RDF field 'Incidence_Angle' (alias RR_ANGLE). As discussed in the GVHDR.XML file, the group of radiometry observations used in this row forms a 'cohort'. Within a cohort, the incidence angle of each observation falls within a single interval of size 90/N, where N is the value of 'RDF Cohort Incidence Count' from the GVHDR file. We can reconstruct that interval by noting that the average incidence angle of all the observations (given in this column) falls within the same interval. Specifically, we find a value of I that satisfies I * 90.0 / N less than or = 'Incidence Angle' less than (I+1) * 90.0 / N where N = 'RDF Cohort Incidence Count' I = integer between 0 and N-1 inclusive The incidence angles of all observations in the cohort lie in the interval [I*90 , (I+1)*90], and their average value is given in this column. Polarization Angle 4 7 UnsignedByte 1 degree 0.72 -90 The average polarization angle of the received radiation. The polarization angle is defined to be +/- 90 degrees for H-H polarization (+90 is nominal for mission cycle 1) and 0 degrees for V-V polarization. Nearly all orbits maintained an almost constant H-H or V-V polarization angle; the values of 90 or 0 reported for these orbits are only nominal and are not based on actual geometric calculations. Only values that differ from 90 or 0 have been actually computed. Emissivity Variance 5 8 UnsignedByte 1 0.016000 -5 The unbiased estimate of the variance of the emissivity. The emissivity is obtained from the 'Surface_Emissivity' field (alias RR_EMISS) in the ARCDR. The variance estimate gives an indication of the variation in emissivity across the pixel. The unbiased estimate is obtained from the following formula: 'Emissivity Variance' = 1/(N-1) * ( SUM(X_i^2) - 1/N * [SUM(X_i)]^2 ) where N = 'Sample Count' above X_i = samples of radius RR_EMISS, i = 1,2,...,N. The value in the table is the base-10 logarithm of the actual value. To recover the actual value, apply the scaling and offsets given above to the column value, and raise 10 to this power. Emissivity 6 9 UnsignedMSB2 2 0.000015260 The average emissivity estimate. The emissivity value for each footprint is obtained directly from the ARCDR RDF field 'Surface_Emissivity' (alias RR_EMISS). At the moment, the measurements are not weighted based on the footprint center's distance from the pixel center. gvrdf.lbl 0 PDS3 Original PDS3 label Carriage-Return Line-Feed gvrdf.fmt 0 PDS3 Original PDS3 format file Carriage-Return Line-Feed