An Assessment of the Altimetric Information Derived from Spaceborne SAR (RADARSAT-1, SRTM3) and Optical (ASTER) Data for Cartographic Application in the Amazon Region

Abstract

Difficulties in acquiring a complete aerial photography coverage on a regular basis in the Brazilian Amazon due to adverse environmental conditions affect the quality of the national topographic database. As a consequence, topographic information is still poor, and when available needs to be up-dated or re-mapped. In this research, altimetric information derived from RADARSAT-1 (Fine and Standard modes), SRTM3 (3 arc-seconds) and ASTER (band 3N-3B) was evaluated for topographic mapping in two sites located in the region: Serra dos Carajás (mountainous relief) and Tapajós National Forest (flat terrain). The quality of the information produced from Digital Elevation Models (DEMs) was evaluated regarding field altimetric measurements. Precise topographic field information acquired from Differential Global Positioning System (DGPS) was used as Ground Control Points (GCPs) for the modeling of the stereoscopic DEMs (RADARSAT-1, ASTER) and as Independent Check Points (ICPs) for the calculation of accuracies of the products. The accuracies were estimated by comparison of the DEMs values and real elevation values given by ICPs. The analysis was performed following two approaches: (1) the use of Root Mean Square Error (RMSE) for the overall classification of the DEMs considering the Brazilian Map Accuracy Standards (PEC) limits and, (2) calculations of trend analysis and accuracy based on a methodology that takes into account computed discrepancies and standard deviations. The investigation has shown that for flat relief, the altimetric accuracy of SRTM3 and Fine RADARSAT-1 DEMs fulfilled the PEC requirements for 1:100,000 A Class Map. However, for mountainous terrain, only the altimetry of SRTM3 and ASTER fulfilled these requirements. In addition, the performance of ASTER was slightly superior to SRTM3. However it is important to consider the difficulties in the acquisition of good stereo-pairs with optical data in the Amazon and the additional cost (GCPs) to produce ASTER DEMs. Despite showing systematic errors, the findings justify the usage of SRTM3 as a primary elevation source for semi-detailed topographic mapping in the region. It is suggested a combination of altimetry derived for SRTM3 and planimetry extracted from high-resolution SAR (ALOS/PALSAR, TerraSAR-X, RADARSAT-2) or if available optical data for semi-detailed topographic mapping programs in the Brazilian Amazon, where terrain information is seldom available or presents low quality.

Evaluation of the altimetry from SRTM-3 and planimetry from high-resolution PALSAR FBD data for semi-detailed topographic mapping in the Amazon Region

“…In addition, no bias was detected for the interferometric DSM, while a systematic offset (bias) in planimetry is present for the N component in the PALSAR ortho-images mosaics. These findings are in accordance with previous results in the literature, which emphasized the quality of both sources of data (SRTM-3 and PALSAR-FBD) for semidetailed topographic mapping purposes (Jarvis et al 2004, Rodriguez et al 2005, Cheng 2007, Oliveira and Paradella 2008.…”

“…The first evaluation of the altimetric quality from SRTM-3 (3 arc-seconds by 3 arc-seconds), in flat and mountainous relief of the Brazilian Amazon, has indicated a RMSE of 12 m in elevation that fulfilled the topographic mapping requirements for 1:100,000 A Class map. These findings justified the choice of SRTM-3 data as a primary elevation source for semidetailed topographic mapping in the region (Oliveira and Paradella 2008). However, it is important to mention that, for cartographic production, updated planimetric information is also necessary.…”

“…On the other hand, results related to SRTM-3 (3 arc-seconds by 3 arc-seconds) in Ecuador, Honduras and Colombia indicated an average error of 8 m in elevation (Jarvis et al 2004). Finally, results from Oliveira and Paradella (2008) indicated elevation errors (90% of probability) of 19 and 21 m, respectively, for flat and mountainous relief in the Brazilian Amazon. The SRTM-3 data used in this research were acquired at ftp://e0srp01u.ecs.nasa.gov/srtm/version2/SRTM3 in Lat/Long coordinates related to the World Geodetic System 1984 (WGS84) ellipsoid and the Earth Gravitational Model 1996 (EGM96) vertical datum and available in HGT file format.…”

“…These results partly fulfilled the national Map Accuracy Standards elevation requirements for 1:100,000 A Class. On the other hand, the altimetry produced from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo-pairs was better and indicated a RMSE around 10 m in elevation for mountainous terrains (Oliveira and Paradella 2008). However, adverse atmospheric conditions in the Amazon region preclude the generalized use of ASTER images for systematic basis coverage.…”

Caracterização morfométrica de bacias hidrográficas através de dados SRTM

“…Santos et al (2006) notaram que o MDE obtido a partir de dados SRTM apresentou melhores resultados altimétricos quando comparado com o MDE gerado a partir de cartas topográficas escalas 1:100.000. Oliveira & Paradella (2008) estudando uma área de relevo plano e montanhoso da região Amazônica, concluíram que o MDE derivado do SRTM atendeu aos padrões de exatidão cartográficos para a escala de 1:100.000 Classe A.…”