)0K DIRECTION
7 8 9
* \ /
7~7—r-?- r -r~r-?
/ /
LOUGHED STRIP
1 2
grass surface
>rs in the
er barbed wire
ew metres wide
iivide. Farther
s grass cover,
on on 23 June
lar in X and C
over the test
rocessed (high
obtained over
able in X- and
2° towards the
only in C-band
and during the
respectively,
if drum reflec-
ght patches by
film has been
3x enlargement
:he transparen-
lears as a dark
s could be ex-
ction. On both
as occur repre
shallow depres-
his is followed
(urface texture,
which separates
ivide. The fire
s of the rough-
OK DIRECTION
3 LOUGHED STRIP
'—' 1 2(?)
ilectors on
tted)
ness of the ploughed bare soil surface. The back
ground tone of the grass field surrounding the drum
reflectors is uniform and relatively dark as a
result of the low scattering.
On the radar strip 77 C-band, most drum reflec
tors can be differentiated under the microscope, as
shown in fig. 3. Their size and separation were
measured with a micrometer.
Drum reflectors 1 and 2 are 4 m apart and can be
seen as two different point targets. The same is
true for 2 and 3. Target points 3 and 4 are separa
ted only 2 m in the field but appear on the image
as two separate targets roughly 3 to 4 m apart,
whereas drum reflectors 4 and 5, which are also 2 m
apart, are hardly separable on the image. All five
targets have the same orientation, horizontal, and
not inclined towards the incoming radar beam. There
is no indication for the reason why the first two
targets gave less backscatter than the third one.
Drum reflectors 6 and 7 are only 1.5 m apart and
could not be seen as separate targets, but appear
as one large blob. Reflectors 8 and 9, on the other
hand, which are 2 m apart, can be seen as two dif
ferent targets. Reflectors 10 and 11 also gave high
returns, but 12 is not discernible. The approximate
2 m azimuth resolution for these targets confirms
the data given by Intertech.
Fig. 4 Radar response drum-reflector field as seen
under a 63X microscopic enlargement (3rd
generation optically correlated imagery):
a. Strip 78X under 32° depression angle
b. " 77C " 42°
c. " 76C " 70°
Strip 76 C-band gives a distribution of point
targets as sketched in fig. 4c. Most of the drum
reflectors seem to be present in the image under
the microscope and their site and separation is
more or less according to scale. The alignment of
the drums, however, is absent, and the image seems
to suffer some distortion.
On strip 78 X-band, the drums are not well defined
point targets, but appear to be smeared out in range
direction over distances of approximately 10 m. This
seems to occur over the entire image. In azimuth
directions, a number of the aligned point targets
can be separated, although it is difficult to
assign numbers to the blobs (fig. 4a).
Of reflectors 1-5, at least 4 seem to be present
and separable, and of 6-9, at least 2. This agrees
wit an azimuth separation of about 2 metres. The
range resolution, however, is far less for the X-
band (about 10 m) than for the C-band (about 2m).
As no more X-band images are available over the
site, no conclusion is warranted if range resolu
tion is far below specification on all X-band
images.
The following is a summary of the results yielded
by the four radar strips.
Strip 78 X-band, depression angle 32°: Drums not
well-defined point targets, range resolution ± 10 m
azimuth resolution ± 2 m.
Strip 78 C-band: Drums reasonably defined point
targets, range resolution ± 2 m, azimuth resolution
± 2 m.
Strip 77 C-band, depression angle 42°: Drums
well-defined point targets, range and azimuth reso
lution better than 2 m.
Strip 76 C-band, depression angle 70°: Drums
reasonably defined point targets, range distortion:
no proper alignment, azimuth resolution ± 2 m.
CONCLUSION
As a conclusion, it can be stated that oil drums
cut in half can be used as point targets for
assessing spatial resolution. They are detectable
on the radar image. Care must be taken that a uni
form low-response background is present. A smooth
grass or sand surface is good for this. A number of
these drums, oriented with respect to radar look
direction, should be placed in a recognisable con
figuration so that it is possible to locate them on
the radar images. Working with digital data makes
quantification easier: nevertheless, optically
processed data studied under high magnification can
give good quantitative insight into the ground
resolution and image quality of the system. Such a
test site can be cheaply set-up, even in developing
countries, and can serve as a test site at the
beginning and end of each flight mission during a
radar survey campaign.
REFERENCES
Forshaw, M.R., A. Haskell, P.F. Miller, D.J.
Stanley and J.R. Townshend 1980. A review paper:
Spatial resolution of Remotely Sensed Imagery.
U.S. Committee Peaceful Uses of Outer Space, 53
pp.
Intertech Remote Sensing Ltd., 1981. ESA/JRC SAR
580 campaign system specification document.
Intertech report 951-81-1.
Koopmans, B.N., C. Anton Pacheco, T. Woldai and A.
Payas, 1985. SARTHI: A side-looking radar survey
over the Iberian Pyrite Belt. Investigators final
report Vol. 2. The European SAR-580 Experiment
JRC/ESA publ. SA.1.04.E2.85.12/2, p. 125-149.
Smith, D.J. Quality assessment of SAR-580 pro
ducts. Investigators final report Vol. 1. The
European SAR-580 Experiment JRC/ESA publication
SA.1.04.E2.85.12/1, p. 63-69.
