Flood monitoring in South America from the Landsat NOAA and nimbus satellites

Abstract

Since shortly after its launch in 1972, Landsat imagery has been used by hydrologists and engineers to monitor floods on an experimental basis. Employing multispectral scanner (MSS) data, with a 185-km swath and 80-m ground resolution, flooded areas were mapped at scales as large as 1:250,000. Numerous research papers described this application of satellite imagery to floods, but to be useful in operational hydrology, timing becomes increasingly important. Imagery--ideally--should be collected shortly after the flood has peaked, but the Landsat repeat data collection cycle is 16 days (8 days when two satellites are operating). Unlike Landsats-1, -2 and -3, the “skip” orbit of Landsats-4 and -5 commonly precludes monitoring of regional flooding that extends to adjacent swaths. From late 1982 to late 1983, severe flooding occurred in the Valley of the Parana River of South America. As part of a post-flood study made for the Organization of American States of all available satellite flood imagery, an archival search yielded only a few usable Landsat images of the lower reach of the Parana River in Argentina. The NOAA satellite archives of Advanced Very High Resolution Radiometer (AVHRR) data were suprisingly sparse owing to infrequent coverage and frequent cloudiness, and yielded no usable imagery. However, coastal-zone color scanner (CZCS) data were available over the study area, but the CZCS had never before been used in flood studies. The CZCS is a 6-band radiometer with a 1,636-km swath. Ground resolution is 825 m at nadir. Employing data collected by Nimbus-7 on 24 June 1983, near the peak of the flood, multispectral color images using two of the six bands were prepared digitally. Three subscenes were mosaicked to show a 70-km reach of the river in which the width of flooding ranged from 20 km to 70 km in the Valley of the Parana. AVHRR imagery collected by NOAA-9 in November 1985, which was successfully used to map the extent of coastal flooding caused by Hurricane Juan along the Louisiana Gulf Coast at a scale of 1:1,000,000, is also discussed. Although the Nimbus-7 CZCS was designed primarily for oceanographic applications and NOAA-8 and -9 AVHRR for meteorological applications, imagery from both--with their wider swath and greater frequency of coverage--can supplement or substitute for the higher resolution Landsat MSS data.