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Flávio Jorge Ponzoni 
  
EVALUATION OF THE “SALAR DE UYUNI/BOLIVIA” AS RADIOMETRIC CALIBRATION TEST SITE FOR 
SATELLITE SENSORS 
Flavio Jorge PONZONI 
Instituto Nacional de Pesquisas Espaciais (INPE) - Divisio de Sensoriamento Remoto 
Avenida dos Astronautas, 1758 - 12227-010 - Sao José dos Campos SP - Brasil 
flavio@ltid.inpe.br 
Rubens LAMPARELLI, Giampaolo Queiroz PELLEGRINO, Jurandir ZULLO JUNIOR 
Universidade de Campinas (UNICAMP) - Centro de Ensino e Pesquisa em Agricultura (CEPAGRI) 
Cidade Universitária "Zeferino Vaz"- Baráo Geraldo - Campinas SP - Brasil 
rubens € cpa.unicamp.br, giam cpa.unicamp.br, jurandir@cpa.unicamp.br 
  
KEY WORDS: Radiometric calibration, calibration, satellite sensors 
ABSTRACT 
The “Salar de Uyuni”(Bolivia) has been pointed out as a potential reference site for spectral calibration purposes (Price, 
1987). TM/Landsat 5 images from 1988 to 1997 were used in order to evaluate the spectral characteristics of the “Salar de 
Uyuni” surface. It was considered images of six TM spectral bands (band 1, 2, 3, 4, 5 and 7) which were used to calculate 
Variation Coefficients (VC) values for each pixel in each spectral band. These VC values were exchanged by color tones 
and VC images were created. It was possible to evaluate the spectral stability of the “salar” surface for each TM band 
through the VC images. The results have pointed out that the “salar” surface is not so stable as could be firstly 
supposed, mainly in infrared region in which surrounding areas were identified as more stable for this spectral region. 
Radiometric measurements were performed in field in order to compare them to orbital data. 
1INTRODUCTION 
The substantial increasing on the number of operational and to-launch satellites and on the quantitative use of its 
information requires a parallel increasing of the knowledge about radiometric behavior of the remote sensors along time. 
They may suffer changes that should be monitored by periodic calibrations. The calibration methods for natural resource 
satellites can be grouped in two parts: (a) the pre-launch methods based on laboratory measurements and (b) the post- 
launch methods based on the observation of celestial bodies (like Sun and Moon) or earth surface targets. 
The use of terrestrial targets or calibration sites is the one that presents best results along the satellite lifetime. All 
calibration sites used or proposed until now are located on north hemisphere like: White Sands (USA), La Crau (France), 
Sahara and Gobi deserts (respectively on Africa and China). A completely different calibration site in localization (i.e., 
south hemisphere) and surface type has been suggested by many authors (like Price, 1987) as an ideal alternative for 
satellite sensors calibration: the Uyuni salt lake in Bolivia called as “Salar de Uyuni”. It is a flat area of about 200 x 100 
km, at 3700 meters of altitude and covered homogeneously by salt. This means the biggest and higher salty open area in 
the world. According to literature, the “Salar de Uyuni” has very good characteristics for using it for calibration 
purposes: small atmospheric influence, spectral stability, high reflectivity and proximity to a contrasting target that is the 
Titicaca Lake. On this context, the objective of this paper is to analyze the radiometric changes on the Lansat-5/TM 
satellite sensor along time, and to radiometricaly characterize the “Salar de Uyuni” in order to evaluate it as a sensor 
calibration site in south hemisphere. 
2METHODOLOGY 
2.1 Study area localization 
The “Salar de Uyuni” is located in the bolivian “altiplanos”, at 3700 meters of altitude, and has a surface of about 200 x 
100 km covered homogeneously by salt. The Salar is inside a area delimited by the following geographical coordinates: 
20°40°S, 68*17"W, 19? 45" S and 66? 45"W, as shown in Figure 1. 
The Salar de Uyuni is the largest salt flat in the world with an area of 9000 square kilometers. Located on the central 
Andean Altiplano of Bolivia, it is at an elevation of over 3600 meters. The Salar is a structurally depressed basin 
bordered by the Cordillera Occidental to the west and the Cordillera Oriental to the east. The Salar is partially filled with 
alluvial and glacial deposits and is underlain by Tertiary and Quaternary rhyolitic ashflow tuffs. The surface of the Salar 
is an evaporate crust of predominantly porous halite and up to 10m thick. Due to the repeated wet and dry cycles, the 
surface of the Salar is exceptionally smooth with relief measured in centimeters. Situated in a semiarid climate, the Salar 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000. 231