SEASAT and GEOSAT Altimetry Data for the Antarctic and Greenland Ice Sheets

Variables

Elevation Grid Header Record

Bytes	FORTRAN Variable Type	Description
1-4	I*4	Number of i values in the grid
5-8	I*4	Number of j values in the grid
9-12	I*4	Starting north latitude of grid in degrees North (x 10^6) (this will be approximate for a polar stereographic grid)
13-16	I*4	Starting east longitude of grid in degrees East (x 10^6) (this will be approximate for a polar stereographic grid)
17-20	I*4	Ending north latitude of grid in degrees North (x 10^6) (this will be approximate for a polar stereographic grid)
21-24	I*4	Ending east longitude of grid in degrees East (x 10^6) (this will be approximate for a polar stereographic grid)
25-28	I*4	Status word for data used to generate grid. A zero in any bit position indicates that the correction is not applied.

Bits	Value	Description
0-23		Unused
24	1	Slope correction applied
	0	Slope correction not applied
25		Unused
26	1	Solid tides removed
	0	Solid tides not removed
27	1	Retracking correction applied
	0	Retracking correction not applied
28	1	Center of gravity bias applied
	0	Center of gravity bias not applied
29	1	Tropospheric correction applied
	0	Tropospheric correction not applied
30	1	Ionospheric correction applied
	0	Ionospheric correction not applied
31	1	Time bias applied
	0	Time bias not applied

29-32	I*4	Polar stereographic grid size conversion and scaling factor from half-inch grids on projection plane to the desired grid size (x 10^6)
33-36	I*4	The number of grids of desired size from the pole to the equator based on the grid size conversion and scaling factor (x 10^6)
37-40	I*4	Latitude of the map perimeter in degrees North (x 10^6)
41-44	I*4	Greenwich orientation in degrees (x 10^6)
45-48	I*4	Polar stereographic switch =0: Grid has constant increment in latitude, longitude =1: Grid is in polar stereographic projection
49-52	I*4	Number of I-axis divisions to the extent of the map perimeter
53-56	I*4	Number of J-axis divisions to the extent of the map perimeter
57-60	I*4	J coordinate of the projected pole
61-64	I*4	I coordinate of the projected pole
65-68	I*4	Minimum J index of the grid
69-72	I*4	Maximum J index of the grid
73-76	I*4	Minimum I index of the grid
77-80	I*4	Maximum I index of the grid
81-180		Padded to keep same size as data records

Elevation Grid Data Records

Bytes	FORTRAN Variable Type	Description
1-4	I*4	Condition number of the matrix used in the least squares solution to the function (x 10^6)
5-8	I*4	Capsize in degrees latitude -- radius from grid location defining area from which data was used to define grid (x 10^6)
9-12	I*4	North latitude of grid point in degrees (x 10^6)
13-16	I*4	East longitude of grid point in degrees (x 10^6)
17-20	I*4	Height values of the grid at location relative to sea level in meters (x 10^5)
21-24	I*4	Number of data values that were used to calculate grid value
25-28	I*4	Number of parameters used to define function, NPT, (equals 0, 3, or 6) 0 indicates a nondefined grid value
29-52	I*4	Six gridding function coefficients If NPT is < 6, then the rest of the coefficients are initialized to zero (x 10^5)
53-76	I*4	Set of null coefficients associated with any negligible singular values If NPT is < 6, then rest of coefficients are set to zero (x 10^6)
77-80	I*4	Distance in kilometers from grid locations to closest data point (x 10^6)
81-84	I*4	North latitude of closest data point to grid location in degrees (x 10^6)
85-88	I*4	East longitude of closest data point to grid location in degrees (x 10^6)
89-92	I*4	Height associated with closest data point to grid location in meters (x 10^5)
93-96	I*4	Standard deviation of the data with respect to the gridding function in meters (x 10^6)
97-180	I*4	Correlation matrix from solution This is a symmetrical 6 X 6 matrix, so only the upper triangular portion is stored The order of storage: Elements 1-6 are the first row elements; 7-11 columns are 2-6 of the second row, etc. (x 10^5)

Georeferenced Database Header Record

Bytes	FORTRAN Variable Type	Description
1-4	I*4	Number of latitude rows in the database
5-8	I*4	Northwesternmost latitude of database in degrees North (x 10^5)
9-12	I*4	Northwesternmost longitude of database in degrees East (x 10^5)
13-16	I*4	Southeasternmost latitude of database in degrees North (x 10^5)
17-20	I*4	Southeasternmost latitude of database in degrees East (x 10^5)
21 to NROWS*4-1	I*4	Width of each latitude row in degrees (x 10^5), starting with the southernmost row This is dimensioned by the number of latitude rows in the database
next NROWS*4	I*4	The number of longitude divisions in each latitude row, starting with the southernmost row This is dimensioned by the number of latitude rows in the database
next 4 bytes	I*4	Logical record number in database at which directory starts
next 4 bytes	I*4	Unused
next 4 bytes	I*4	Maximum latitude of data (may not be equal to value in bytes 5-8 if data is subarea of the total bin configuration area) in deg N (x 10^6)
next 4 bytes	I*4	Minimum longitude of data (may not be equal to value in bytes 5-8 if data is subarea of the total bin configuration area) in deg E (x 10^6)
next 4 bytes	I*4	Minimum latitude of database (may not be equal to value in bytes 13-16 if data is subarea of the total bin configuration area) in deg E (x 10^6)
next 4 bytes	I*4	Maximum longitude of database (may not be equal to value in bytes 17-20 if data is subarea of the total bin configuration area) in deg E (x 10^6)
next 20 bytes	C*20	Character data description of orbit used in calculation of surface height in database
next 4 bytes	I*4	YYMMDD database beginning time
next 4 bytes	I*4	HHMMSS database beginning time
next 4 bytes	I*4	YYMMDD database ending time
next 4 bytes	I*4	HHMMSS database ending time
next 4 bytes	I*4	Mission word

Bits	Value	Description
0-25	0	Unused
26	1	GEOS-C data included
	0	GEOS-C data not included
27	1	ERS-1 data included
	0	ERS-1 data included
28	1	TOPEX data included
	0	TOPEX data not included
29	1	GEOSAT-ERM data not included
	0	GEOSAT-ERM data not included
30	1	GEOSAT-GM data included
	0	GEOSAT-GM data not included
31	1	Seasat data included
	0	Seasat data not included

next 4 bytes	I*4	Mission status word for Seasat
next 4 bytes	I*4	Mission status word for GEOSAT-GM
next 4 bytes	I*4	Mission status word for GEOSAT-ERM
next 4 bytes	I*4	Mission status word for TOPEX
next 4 bytes	I*4	Mission status word for ERS-1
next 4 bytes	I*4	Mission status word for GEOS-C

Mission status words for altimetry data:

Bits	Value	Description
0-22	0	Unused
23	1	Ocean tides removed
	0	Ocean tides not removed
24	1	Slope correction applied
	0	Slope correction not applied
25	1	Orbit adjustment 1 applied
	0	Orbit adjustment 1 not applied
26	1	Solid tides removed
	0	Solid tides not removed
27	1	Retracking correction applied
	0	Retracking correction not applied
28	1	Center of gravity bias applied
	0	Center of gravity bias not applied
29	1	Tropospheric correction applied
	0	Tropospheric correction not applied
30	1	Ionospheric correction applied
	0	Ionospheric correction not applied
31	1	Time bias applied
	0	Time bias not applied

Georeferenced Database

Subgroup 1: One logical record for each bin containing data

Bytes	FORTRAN Variable Type	Description
1-4	I*4	Indicates the number of logical records that follow which are located in the bin
5-32		Unused

Subgroup 2: One logical record for each data point in the bin

Bytes	FORTRAN Variable Type	Description
1-4	I*4	North latitude of datum point in degrees (x 10^6)
5-8	I*4	East longitude of datum point in degrees (x 10^6)
9-12	I*4	Surface height relative to the ellipsoid in centimeters
13-16	I*4	Height sigma, arbitrary value of 1.0 meter used (x 10^5)
17-24		Reserved for future use
25-28	I*4	Rev number
29-32	I*4	Slope correction in meters (x 10^5) <(-999999999 if unavailable)

Subgroups 1 and 2 are repeated for as many bins with data.

Georeferenced database bin directory

Bytes	FORTRAN Variable Type	Description
1-4	I*4	Record number at which data for bin 1 starts
5-8	I*4	Record number at which data for bin 2 starts
9-12	I*4	Record number at which data for bin 3 starts
13-16	I*4	Record number at which data for bin 4 starts
17-20	I*4	Record number at which data for bin 5 starts
21-24	I*4	Record number at which data for bin 6 starts
25-28	I*4	Record number at which data for bin 7 starts
29-32	I*4	Record number at which data for bin 8 starts

Note: The directory contains as many 32-byte logical records as necessary to designate the record locations of all bins. Any geographical bin for which there is no data has a 0 put in as the starting record number.

Service Interruption

National Snow and Ice Data Center

Variables