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2. SOUTH AMERICA
2.4 Annual flooding patterns of the Amazon
river
It is of great scientific interest to monitor the annual
flooding patterns of the Amazon river and its tributaries.
The water level of the rivers may change with as much as
10 meters between the low water mark and the peak of
flood and given the relatively modest topography in the
basin, this results in extensive flooding of large areas.
The annual flooding have direct or indirect implications on
such diverse issues as algae production in the river food
chain, spatial distribution of flora and fauna or natural
release of green house gases (methane).
In contrast to optical sensors and short wave length SAR,
L-band SAR has proved efficient in detecting standing
water beneath the forest canopy. The longer wave length
signals penetrate the canopy, have a corner reflector
type reflection on the trunks and the water surface and
return to the satellite with little loss. This results in a
brighter backscatter than for non-flooded forest where
the exposed rough ground cause a more lossy diffuse
scatter. Given this important property of the satellite and
the scientific interest in flooded environments, it was
decided to map the Amazon basin not only one time, but
twice - once during the low water and once during high
water.
2.2 Coverage and data acquisition schedule
The data acquisitions over South America cover the
northwestern part of the continent, latitude South 14° -
North 12° and longitude West 50° - 80°. This covers the
entire catchment basin of the Amazon river, including the
Brazilian states of Amazonas, Para, Roriama, Acre,
Rondónia and parts of Mato Grosso. Included are also
French Guiana, Surinam, Guyana, Venezuela, Colombia
'and parts of Peru and Bolivia. This amounts to a total area
of about 8 million km2, or. more than 2000 scenes. These
figures refer to one full coverage - multi-temporal mapping
at low and high flood consequently double the figures to
16 million km2, or almost 4500 scenes.
The low water coverage of the entire area was performed
in one sweep from late September to early December,
1995, aiming to coincide with the annual low peak of the
river. Incidentally, the lowest water level recorded in the
Amazon in decades occurred in October 1995, very
timely indeed.
The high water coverage is planned for early May to late
July, 1996. With some more luck, we might hit another
Stage record...
2.3 Ground truth verification
Ground truth measurements in the field were performed
simultaneously with the satellite acquisitions. The
activities included both videography and photography
from a small aeroplane along a number of pre-determined
flight lines as well as ground based measurements at
595
Figure 1. GRFM coverage over South America
areas or transects of specific interest. During the low
water coverage, the efforts were concentrated to areas
within 1-2 days of reach from the town of Manaus in the
central part of Amazonas (Anavilhanas, Balbina,
Cabaliana, Mamiruá, Marchantaria, Rio Madeira, Rio Jaü,
Xiborena). During the high water acquisitions, these
areas will be complemented by field work in and around
Rondónia and Rio Tapajos.
The field activities were performed by NASDA, the
National Institute for Space Research of Brazil - INPE,
the National Institute for Amazonian Research of Brazil -
INPA (partially sponsored by NASA), Petrobrás/CENPES,
University of California Santa Barbara - UCSB (sponsored
by NASA) and the Jet Propulsion Laboratory - JPL
(sponsored by NASA).
2.4 Data processing
2.4.4 Raw data processing: The data recorded
onto the satellite Mission Data Recorder were down-linked
either at NASDA Earth Observation Center in Hatoyama,
north of Tokyo, or at the Alaska SAR Facility (ASF) in
Fairbanks, Alaska. Financed by NASA, raw data
processing of all 4500 scenes will be performed by ASF.
The low water season batch will be processed during the
spring and summer of 1996 with the high water batch
following on after that. The output data will be standard
ASF high resolution scenes, i.e. ground range, amplitude,
8 bits scenes at 12.5 meter pixel size.
2.4.2 Generation of low resolution data: The
high resolution scenes will be handed over to the Jet
Propulsion Laboratory in Pasadena, California for post
processing (sponsored by NASA). This step includes
downsampling of each of the large 12.5 meter scenes to
low resolution scenes at 100 meter pixels. Downsampling
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
