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6.6.9 Geolocation Grid ADSRs
The Geolocation Grid is a table which lists the
slant range time, incidence angle, and geodetic
latitude and longitude positions at various
range/azimuth positions within the image. The
location of each tie point (or grid point) in
the image is specified by
a line and
sample co-ordinate system. Tie point locations
in azimuth are specified using the Zero Doppler
Time stamp found at the start of each range
line in the MDS. The location in range is
specified by the number of range samples. Tie
points must
be placed at points
corresponding to an integer number of range
samples, and tie points must be located at least
the following 3 points within those
reported: the first range sample of the range
line, the mid swath range sample, and the last
range
sample of the range line.
For Geocoded products, the Zero Doppler Time
stamp does not apply. Therefore, it is set to
zero, and only the range line number is used
to index the grid entries. The grid
spacing in azimuth defines the granule size of the
ASAR product. That is, a grid line provides tie
points for the first line and last line of a
granule. There will be 11 grid updates in range per
ADSR. In azimuth, a new ADSR will be added to the
ADS nominally every:
- 10 km in azimuth for IM and AP;
- 40 km in azimuth for WS and GM.
The contents of a Geolocation Grid ADSR
are shown below:
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Table 6.45 Geolocation Grid ADSRs
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|
#
|
Description
|
Units
|
Count
|
Type
|
Size
|
|
Data Record
|
|
0
|
first_zero_doppler_time
Zero doppler
time in azimuth of first line of
the granule Gives
azimuth location of grid
line for first line of the granule.
|
MJD |
1 |
mjd |
12 byte(s) |
|
1
|
attach_flag
Attachment Flag
Set to 1 if all MDSRs
corresponding to this ADSR
are blank, set to zero otherwise
|
flag |
1 |
BooleanFlag |
1 byte(s) |
|
2
|
line_num
Range line
number corresponding to the
first line of the granule within
the slice.
Warning: (1) This is not
always the record number of
the corresponding image
MDSR. Use the number of
lines per granule field to
determine the image MDS
record corresponding to each
record of tie points.(2) For
a stripline product, which
may consist of multiple
slices in a single MDS, this
number is reset to 1 at the
beginning of each slice.(3)
For child products, which
are subsets of a full
product, the range line
number in the first record
may not be 1.
|
- |
1 |
ul |
4 byte(s) |
|
3
|
num_lines
Number of output
lines in this granule |
lines |
1 |
ul |
4 byte(s) |
|
4
|
sub_sat_track
Subsatellite
track heading (relative to
North) for first line of granule
This is the heading on
the ground (includes Earth rotation)
|
deg. |
1 |
fl |
4 byte(s) |
|
5
|
first_line_tie_points
First Line Tie
Points The
following fields each
contain 11 values
corresponding to 11 tie
points in the first line of
the granule
|
- |
1 |
first_line_tie_pointsStruct |
220.0 byte(s) |
|
|
a
|
samp_numbers
Range sample
number Gives the
range location
of the grid
points. First
range sample is
1, last is M |
- |
11 |
ul |
11*4 byte(s) |
|
b
|
slant_range_times
2 way slant
range time to
range sample |
ns |
11 |
fl |
11*4 byte(s) |
|
c
|
angles
Incidence Angle
at range sample |
deg. |
11 |
fl |
11*4 byte(s) |
|
d
|
lats
geodetic
latitude
(positive north) |
(1e-6) degrees |
11 |
GeoCoordinate |
11*4 byte(s) |
|
e
|
longs
geodetic
longitude
(positive east) |
(1e-6) degrees |
11 |
GeoCoordinate |
11*4 byte(s) |
|
|
6
|
spare_1
Spare |
- |
1 |
SpareField |
22 byte(s) |
|
7
|
last_zero_doppler_time
Zero doppler time
for the last line of the granule |
MJD |
1 |
mjd |
12 byte(s) |
|
8
|
last_line_tie_points
Last Line Tie
Points The
following fields each
contain 11 values
corresponding to 11 tie
points in the last line of
the granule
|
- |
1 |
last_line_tie_pointsStruct |
220.0 byte(s) |
|
|
a
|
samp_numbers
Range sample
number Gives the
range location
of the grid
points. First
range sample is
1, last is M |
- |
11 |
ul |
11*4 byte(s) |
|
b
|
slant_range_times
2 way slant
range time to
range sample |
ns |
11 |
fl |
11*4 byte(s) |
|
c
|
angles
Incidence Angle
at range sample |
deg. |
11 |
fl |
11*4 byte(s) |
|
d
|
lats
geodetic
latitude
(positive north) |
(1e-6) degrees |
11 |
GeoCoordinate |
11*4 byte(s) |
|
e
|
longs
geodetic
longitude
(positive east) |
(1e-6) degrees |
11 |
GeoCoordinate |
11*4 byte(s) |
|
|
9
|
spare_2
Spare |
- |
1 |
SpareField |
22 byte(s) |
DS_NAME : Geolocation Grid ADSRs
Format Version 114.0
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Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,
atmospheric chemistry
|
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