.c.Bebedouro, Brazil


Title of Investigation:

I.  Microwave Remote Sensing Data From a Spaceborne Platform
as a Tool to Monitor the Hydrological Cycle of a Floodplain
Area ("Varzea") at Northeast Brazil.

Principal Investigator:

I.  Dr. Joo Vianei Soares
  Instituto de Pesquisas Espaliers (INPE)

Site Description:

 This experiment will be conducted at the Bebedouro Irrigation
Project, located in the northern Rio So Francisco valley,
northeast Brazil, in the state of Pernambuco, approximately
42 km north of Petrolina (Figures 1, 2, and 3).  The irrigated
area is 1750 ha; the size of individual fields varies between
5 and 12 ha.  The regional climate is classified after Kppen
as Bsh'w-type, with a minimum air temperature of 14C and
a maximum temperature of 39C,  and an average annual precipitation
of 391.5 mm; the relative humidity varies from 56.7 to 67.1%
and the annual evaporation is 2106 mm (De Faria, et al.,
1982).
 Agriculture plays an important economic and social role
in Brazil.  One of the major problems related to Brazilian
agriculture is estimating planting areas and their productivities.
 Remote sensing techniques (Landsat-MSS, TM, and SPOT) have
been useful for performing this work.  Summer crops (December/April)
account for more than 90% of the agricultural production.
 Due to the coincidence of the summer growing season and
the rainy season (precipitation above 1200 mm at the crop-producing
region in southern and southeastern Brazil),  it is difficult
to obtain useful remote sensing data at the visible and infrared
wavelengths on a regular basis.  Spaceborne microwave remote
sensing techniques are considered a potential alternative
to solving this problem.
 Floodplains of major Brazilian rivers have high potential
for the expansion of Brazilian agriculture.  This is especially
true in semi-arid regions in northeastern Brazil where long
drought periods cause many social and economic problems.
 According to M. Alves da Silva, et al., 1981, there are
approximately 800,000 ha of floodplains suitable for irrigation
at the Rio So Francisco valley (a Brazilian south-north
flowing river system).  Of these, approximately 90,000 ha
are operational and 75,000 ha are being implemented.  The
Bebedouro test site includes an experimental irrigation project
which is managed by EMBRAPA/CPATSA (Empresa Brasileira de
Pesquisa Agropecuria/Centro de Pesquisa Agropecuria do
Trpico Semi-rido).  According to studies performed at CPATSA
(M. Alves da Silva, et al., 1981), a major hydrologic problem
related to these floodplains is salinization due to improper
irrigation practices.
 Within this context, irrigation techniques that would integrate
hydrological data are of great relevance.  Microwave remote
sensing techniques are of special interest to estimate surficial
soil moisture, one of the fundamental components of the hydrological
cycle.  The multiparameter characteristics of the SIR-C/X-SAR
experiment, as described in the Shuttle Imaging Radar-C Science
Plan (1986) and the X-SAR Science Plan, are well suited for
the experiment to be conducted at Bebedouro. 

Objectives:

I.  a) Develop an algorithm to monitor the hydrological cycle
over agricultural areas based on  SAR imagery and meteorological
data.

  b) Develop algorithms to classify and enhance digital SAR
images.  These algorithms would be helpful for applications
with future spaceborne SAR systems (EOS, ERS-1, RADARSAT).

  c) Verify the possibility of discriminating among cultures
present at the test site by the time of the SIR-C/X-SAR experiment
and to confirm the qualitative attenuation properties of
the vegetation cover as related to the radar parameters frequency,
polarization, and angle of incidence.

  d) Establish a database on a multiparameter SAR system
relying on soil/vegetation descriptors.

Field Measurements:

I.  In situ data acquisition will include:

  a) Routine meteorological data (i.e. air temperature and
humidity, wind velocity, global radiation, pan evaporation,
precipitation rate and frequency) will be obtained from EMBRAPA/CPATSA
Agrometeorological Station.

  b) Depth of water at the irrigation plot;

  c) Micro-meteorological tower(s) for automatic estimation
of surface fluxes based on a simplified aerodynamic method
following Itier, B., 1981; Perrier, A., et al., 1975; and
Perrier, A., et al., 1976.  These data will be employed for
comparison purposes at local scale.

  d) Soil samples representative of the entire area will
be acquired for granulometric analysis.  

  e) Soil samples (about 10 ha; 100 samples/day) from the
0-5 cm layers from the center of the site will be acquired
for soil moisture measurements following the gravimetric
method of Wang, et al, 1986.  These data will be used to
calibrate SIR-C/X-SAR data.

  f) Acquisition of other relevant agronomic parameters,
such as density of seeding, soil type (pedological maps),
roughness, and estimation or measurement of the Leaf Area
Index (LAI) of cultures.

  g) Acquisition of characteristic curves of the soils available
at CPATSA, of a soil-water profile (by neutron probe sampler),
and of the suction potential profile (by tensiometers) to
confirm the actual characteristic curves and estimate the
representative water content of the soil (W2).

  Ancillary data from airborne and spaceborne sensors will
include:

  a) Surface temperature (1 km x 1 km pixel) from AVHRR/NOAA-7
and ancillary data set to fit the two layer bare soil models
(six images/day can be registered at INPE facilities).

  b) Surface temperature from an airborne infrared radiometer
(Barnes PRT-5).  These ancillary data will be used to fit
the simulated surface temperature (from the two layer method).

  c) Backscattering coefficient to be obtained from a dual
frequency/dual polarization airborne scatterometer (C- and
X-bands), from INPE, if it is operational at the time of
the experiment;

  d) To improve regional monitoring, we will acquire multispectral
images from SPOT or TM by the time of the SIR-C/X-SAR overflight.

  e) Color infrared aerial photographs of the area of interest.



Crew Observations:

1)  Crew Journal:  Document weather, floodplain conditions,
extent of inundation, and the condition of the vegetation
canopy.
 
2) Cameras:  Hercules and the Hasselblad will be used to
photograph the site and particularly the floodplain.

Coverage Requirements:

The minimum coverage requirements for this site are four
(4) passes, preferably from the same direction.

Anticipated Results:

I.  a) Establishment of a methodology to estimate soil moisture
and evaporation rates at a regional scale for irrigation
projects, climatological studies, and as an input to numerical
models for weather forecasting, based on operational SAR
systems such as the Earth Observing System (EOS), envisaged
for the mid-90's;

  b) Development of a data base relying on a multiparameter
SAR system and its interaction with different tropical agricultural
crops; and

  c) Development and acquisition of software for the classification
and enhancement of digital SAR images, which will be helpful
for agricultural and hydrological studies in the future (EOS,
RADARSAT, etc.).