| Instrument:
Rosamond Calibration Array |
 |
|
The Rosamond Calibration Array is
located in the Rosamond Dry Lake outside
of Palmdale, California, a short distance
from the NASA Dryden Flight Research
Center. It was established in the early
1990s for calibration of the NASA AIRSAR
and SIR-C missions, as well as the Japanese
JERS-1 SAR. It is composed of a set
of calibration devices called "Corner
Reflectors." These trihedral corner
reflectors have a well-known radar backscatter
at L-band wavelengths. Figure 1 below
is a picture of a typical reflector.
Figure 1. A typical Rosamond trihedral
corner reflector.
The corner reflectors are aligned East/West
along the southern edge of the dry lake
bed. There are two sets of reflectors:
one set is oriented to be imaged by
a radar flying at a heading of 170 degrees,
and the other set is oriented to be
imaged by a radar flying at a heading
of 350 degrees. These orientations were
chosen for space-borne radars that would
be imaging the array. There are 13 reflectors
on the 170 degree heading, and 10 on
the 350 degree heading. The edge of
each side of the corner reflector is
2.4m long.
The brightness of the corner reflector
is given by the following equation (Ruck,
G.T, D.E. Barrick, W. D. Stuart and
C.K. Krichbaum, Radar Cross Section
Handbook, Vol I, p. 593, Plenum,
1970):
and σ is the radar cross
section, λ is the wavelength,
l
is the length of one side of the trihedral
reflector (for the Rosamond reflectors,
l =2.4m), θinc
is the incidence angle, β is the
elevation angle of the corner reflector
, φ(drift) is
the drift angle of the aircraft, and
α is the difference between the
corner reflector azimuth angle and the
radar flight direction. When UAVSAR
is electronically steering to zero doppler,
φ(drift) = 0.
The position of the vertex of each
corner reflectors was measured very
accurately by differential GPS (see
Figure 2).
Figure 2. Measuring the position of
the vertex of each corner reflector.
(Muellerschoen, 2006)
Figure 3 shows an L-band AIRSAR image
of the Rosamond Calibration Array. This
is a three-frequency overlay, (C-band
is blue, L-band is green, P-band is
red ).
Figure 3. Rosamond calibration array
(AIRSAR image) from 1990.
It is possible to see the shadow of
the corner reflectors in the imagery
displayed with Google Earth over this
area. Figure 4 shows these shadows for
corner reflectors 7, 18, 8, and 19.
Figure 4. Shadows cast by the corner
reflectors are visible in high resolution
optical imagery.
The position (WGS-84 Datum) of each
corner reflector is given below (as
of the end of 2006). Corner reflectors
0-12 are pointed at the 170 degree heading
flight lines, and 13-22 at the 350 degree
heading flight lines.
Table 1. Corner Reflector positions
(as of end of 2006).
|
Corner Reflector #
|
Latitude
|
Longitude
|
Elevation (m)
|
|
0
|
34.796968
|
-118.0965259
|
660.9047
|
|
1
|
34.79976241
|
-118.0870473
|
661.0851
|
|
2
|
34.80523651
|
-118.0874563
|
660.8863
|
|
3
|
34.80534159
|
-118.0819065
|
661.0639
|
|
4
|
34.8054152
|
-118.0763735
|
661.1359
|
|
5
|
34.80549955
|
-118.0707429
|
661.2763
|
|
6
|
34.80558404
|
-118.0652217
|
661.3564
|
|
7
|
34.80566879
|
-118.0596615
|
661.3979
|
|
8
|
34.80575105
|
-118.0540683
|
661.5333
|
|
9
|
34.80581369
|
-118.0489122
|
661.5486
|
|
10
|
34.80592481
|
-118.0433628
|
661.6123
|
|
11
|
34.80602351
|
-118.0376905
|
661.7128
|
|
12
|
34.80604641
|
-118.0322773
|
662.0089
|
|
13
|
34.80519086
|
-118.0844138
|
660.9983
|
|
14
|
34.80543973
|
-118.0789101
|
661.1349
|
|
15
|
34.80551752
|
-118.0733374
|
661.2452
|
|
16
|
34.80554505
|
-118.0679379
|
661.2931
|
|
17
|
34.8055004
|
-118.0624535
|
661.3497
|
|
18
|
34.80568567
|
-118.0563878
|
661.5371
|
|
19
|
34.80572158
|
-118.051812
|
661.4661
|
|
20
|
34.80583692
|
-118.0463532
|
661.5333
|
|
21
|
34.80589992
|
-118.040329
|
661.5585
|
|
22
|
34.80603003
|
-118.0350615
|
661.7884
|
|
