International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
  
reflection). When the satellite is in descendent orbit (North to 
South), the antenna views the west side, when it is in ascendant 
orbit (South to North) the antenna views East. With the date 
acquisition, it is possible to determine the orbit and the antenna 
angle  (http://eus.eoc.nasda.go.jp/euswww). According to 
Luckman et al. (1999), the satellite orbit is very important to 
understand the signal reflected by the target in the JERS- I/SAR 
images. 
Another important parameter to be considered in 
multitemporal acquisition dates is the calibration factor, defined 
according to the image processing date. The calibration factor 
for the images processing for each date interval were provided 
by the JERS-1/SAR constructor. 
‘2. MATERIAL & METHODS 
To make that study, a pilot area containing all Cerrado 
physiognomies, as well as some spots of associated vegetation 
such as SSforest, located a conservation unit, named Pé-de- 
Gigante (47037’W, 21037°S), were used to calibrate 
physiognomies with spectral response in both images: optical 
and L band/SAR. 
That conservation unit has been preserved since 1970 and 
its vegetation is well studied, not only in the field (Batalha, 
1997; Mesquita Jr. 1998; Batalha ef al. 2001), but also through 
optical TM-Landsat images (Mesquita Jr. 1998 and 2003). With 
that information, the contents of each 206 polygons of the 
BIOTA-Cerrado project were analysed using not only JERS- 
1/SAR images but also Terra-MODIS images. 
The pilot area is a conservation unit created in 1970, with 
1,225 hectares. The vegetation comprises all Cerrado 
physiognomies in altitudes raging from 590 to 740 m over the 
Guarani aquifer in the state of Sáo Paulo — Brazil. Climatically, 
the region is classified as a tropical season with wet summer 
and dry winter, which corresponds to the Cwa of Koeppen's 
Climatic Classification. The mean annual precipitation is 1,475 
mm year —1 and the mean monthly temperature is around 23 °C, 
with small variations. Wide daily variations on the temperature 
are observed within a range of 20 °C. According to Mesquita Jr. 
(1998), there are in the study area 599,65 ha of cerrado s.s.; 
404,54 ha of cerrado s.s. with thin herbaceous stratum; 49,11 
ha of cerraddo; and 114,14 ha ofcCampo cerrado, besides other 
associated physiognomies. 
The total study areas are 206 remnants found within 22 
first priority zones (FPZ) as indicated in SMA-SP (1997). 
Those polygons were overlaid in 23 JERS-1/SAR scenes, in 
order to analyse their vegetation contents. These polygons are 
derived originally from the Forest Inventory published by 
Kronka ef al. (1993) and visited in the field by a botany team of 
the BIOTA project. 
Primarily, the physiognomies zones map of the pilot area, 
obtained by Mesquita Jr. (1998) were identified to install 40 
plots, comprising the following physiognomies: 10 from Campo 
Cerrado, 10 from Cerrado s.s., 10 from Cerradáo and 10 from 
SSForest. Those plots were analysed through Landsat NDVI 
images (1999 to 2002) and MODIS NDVI (2000 to 2002). 
Secondly, two SAR images from the JERS-1 satellite 
were used to calibrate the probable physiognomies zones with 
the backscattering response, within the pilot area. The SAR 
image data were supplied by National Space Development 
Agency of Japan, NASDA. 
546 
Samples of matching areas were delimited within the 
image and average backscattering values were extracted. These 
values were then correlated with data of total volume of wood 
(m’/ha), determined during field survey. The microwaves 
radiation is transmitted from the JERS-1 radar antenna and, 
after that, it receives the reflected signal from the earth surface. 
The sigma signal (c) value, which is the ratio of the received 
backscattered energy over the emitted energy, are usually 
expressed in decibels (dB) units but can be converted into 
digital numbers (DN) of a intensity image. The o values were 
obtained using the following equation (Roseqvist, 1997; 
Shimada, 2001): 
c — 10.log (2er) + CF 
n 
DN = digital number of a pixel of a 16bits image 
c = (sigma) is the ratio of received backscattered energy 
over emitted energy 
n = number of pixels sampled 
CF = calibration factor 
Another important parameter to be considered in 
multitemporal acquisition dates is the calibration factor, defined 
according to the image processing date. The calibration factor 
for the JER-1/SAR images processing for each date interval are 
shown in the Table 1. 
Table 1 — Calibration factors according to the date interval 
when the images JERS-1/SAR were processed. Source: 
  
  
Processing Date Calibration Factor (dB) 
Until February 14, 1993 -70,00 
After February 15, 1993 -68,50 
After November 01, 1996 -68,20 
After April 01, 2000 -85,34 
  
NASDA (EORC - Orderdesk) 
Finally, 23 JERS-1/SAR images were transformed in 
averaged o values, for each of the 206 fragment found in the 22 
FPZ, and then compared with the NDVI values, obtained by 
Terra-MODIS images. The MODIS NDVI images were 
processed by EOS-DIS/NASA according to Huete ef al. (1999). 
Figure 2 shows the JERS-1 images after pre-processing 
for each FPZ studied. The whole state of Sao Paulo polygons 
were taken from 1990 and 1992 (Kronka et al, 1993), the 
JERS-1 images from 1995 and 1996, and Terra-MODIS NDVI 
images from November 2000 to June 2002. 
All digital processing was performed using the following 
software: ERDAS Imagine, ARC/VIEW, ERMapper, and ENVI 
licenced to the University of Sao Paulo — Brazil. 
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