Most developing countries require information on agricultural
areas and their monitoring. For cotton production in Senegal,
the national company uses farmers' claims and ground enquiries,
but there is a very high error rate in the yield forecast and
it is impossible to obtain an accurate estimation of production.
In this context, space-derived data from satellites can provide
The present project studies the possibility of crop area monitoring
using ERS-1 data, on Senegal. The main objective is to determine
the possibility of crop detection and mapping especially for cotton,
with a multitemporal data set of radar images and determine appropriate
Throughout the crop cycle, 8 SAR images of the same Track/Frame
were acquired, one on each ERS-1 orbit, from May 95 to January
96. During the crop season, a set of ground measurements was made
on selected test fields (about 160). The measurement consists
of a monthly monitoring of the development for different types
of crop (cotton, peanut, cereal). This is completed by geographical
coordinates measured by GPS.
All the images are superimposed and this multi-temporal data
set is used to study the backscatter. The backscattering coefficients
of different crop types and their temporal variation been analyzed
as a function of crop development stage and the recorded rainfall.
It was found that, for most crop types in this representative
agricultural region in Africa, the vegetation covers appear, for
the C-band SAR, as sparse medium and the radar backscatter result
from the soil backscatter. The difference in the radar backscatter
of different crop types relies mainly on the attenuation of the
soil backscatter by the vegetation. Based on the results of this
analysis, a method of mapping different crop types is developed.
In particular, some grouping of crops (cotton and most cereal,
peanuts and mil) have been necessary. Also, the filtering and
mapping methods have been selected to take into account the small
range of the radar backscatter and their temporal variation.
The results present a map of different crop types and their acreage.
In collaboration with the national company, the result of this
estimation is then compared with complementary information (general
knowledge, statistical information). This final evaluation assesses
the possibility of deriving important information from SAR data
during the crop cycle, whilst the cloud cover over this period
does not enable optical data to be acquired.
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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