Navone, Stella Maris 
  
RADAR AND TM DATA: TOOLS FOR DESERTIFICATION MONITORING IN CALCHAQUIES 
VALLEYS (Argentina) 
S.M. Navone, A. Maggi., E. Palacin and E. Rienzi CIAT-Facultad Agronomia Universidad 
Buenos Aires, Argentina ,Tel.(5411)-4524-8092-fax. .(5411)-4524-8737 
There was 75 % of arid and semiarid lands in the Argentine Republic. Desertification/ land 
degradation increases ,according to the government 650000 hectareas per year. (PNUMA, 1996) 
The region of the Arid Valleys in Argentine , has an approximate area of 14,000,000 ha. The 
Calchaquies Valley, in Catamarca, is within this system. Agriculture in the region is concentrated 
in irrigated oases. From the physiographic and climatic viewpoints, the studied valley is similar to 
other northwest valleys like Fiambalá; Tinogasta and Chilecito . However, while in those valleys 
desertification has been galloping during the last thirty years (Igarzábal, 1974; Navone et al, 1996), 
turning it almost into a vast desert, the Calchaquies valley presents the first symptoms of the 
process. 
A management plan for this valley should be made on the basis of a proper description and 
diagnosis of the different levels of desertification present in the basin. The use of preventive measures 
is very important in the areas not yet affected by degradation processes or showing a minimum 
degree. The objective of this research was to find an enhacement to discriminate the earlier stages of 
desertification through radar and Landsat Thematic Mapper images in this valley 
A diagnosis of the desertification degree was done using through observations and transects 
aplying FAO (1984) methodology . In desertification research ,human and biophisics aspects should 
be integrated. (FAO, PNUMA, Secretariat for Natural Resources and Human Environment, 1995.) 
A dry season radar image was choosen for this study. The filters Flee;Fmode;Fsharp and 
Fgamma were applied . 
The best enhaced radar image obtained by this way was merge with Landsat TM 3,4,5 from dry 
season image .Different methods of combining radar and VIS/IR imagery were proved 
> RGB to IHS transforms, 
» Principal component transform and 
> Multiplicative 
Visual and statistical analysis has been done to determine the accuracy level of the different 
products . For that purpose the desertification map done in the field has been overlapped with the 
enhanced images. 
Besides, we originated a scale (value) in order to determine the coincidence level. 
The best enhaced radar image used to merge with optical image was obtained with Gamma-MAP 
filter 
Visual comparison obtained by overlapping between field map and the four enhanced images 
shows that the image generated aplying Principal Components in an image with 3 bands : radar, 
near infrared and middle infrared band,then Fourier transformation and low pass used has the 
highest coincidence 
Then we obtained the correlation to know the efficiency between the different products 
and the map obtained in the field and ground truth and IHS/radar . 
The r2 value shows that statistically the best product to discriminate the earlier stages of 
desertification in Calchaquies valleys is principal components/radar/inverse fourier 
The whole valley of the Santa Maria river has been subjected to some degree of 
dessertification. In fact, 7096 the valley falls evenly either into moderate to severe or the severe 
category. 
y "The useful image obtained to identificate different desertification map units was principal 
component transform with radar and reverse transform. This product highlight moderate to 
severe degree. The merge of optical and radar data convey both chemical and physical 
information and could prove more useful than either image alone. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 
965