Wetlands of the Amazon River basin are globally significant sources of atmospheric methane. Satellite remote sensing (passive and active microwave) of the temporally varying extent of inundation and vegetation was combined with field measurements to calculate regional rates of methane emission for Amazonian wetlands. Monthly inundation areas for the fringing floodplains of the mainstem Solimõ es/Amazon River were derived from analysis of the 37 GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer from 1979 to 1987. L-band synthetic aperture radar data (Japanese Earth Resources Satellite-1) were used to determine inundation and wetland vegetation for the Amazon basin (o500 m elevation) at high (May-June 1996) and low water (October 1995). An extensive set of measurements of methane emission is available from the literature for the fringing floodplains of the central Amazon, segregated into open water, flooded forest and floating macrophyte habitats. Uncertainties in the regional emission rates were determined by Monte Carlo error analyses that combined error estimates for the measurements of emission and for calculations of inundation and habitat areas. The mainstem Solimõ es/Amazon floodplain (54-701W) emitted methane at a mean annual rate of 1.3 Tg C yr À1 , with a standard deviation (SD) of the mean of 0.3 Tg C yr À1 ; 67% of this range in uncertainty is owed to the range in rates of methane emission and 33% is owed to uncertainty in the areal estimates of inundation and vegetative cover. Methane emission from a 1.77 million square kilometers area in the central basin had a mean of 6.8 Tg C yr À1 with a SD of 1.3 Tg C yr À1 . If extrapolated to the whole basin below the 500 m contour, approximately 22 Tg C yr À1 is emitted; this mean flux has a greenhouse warming potential of about 0.5 Pg C as CO 2 . Improvement of these regional estimates will require many more field measurements of methane emission, further examination of remotely sensed data for types of wetlands not represented in the central basin, and process-based models of methane production and emission.

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Four Validation Over ights for Amazon Mosaics ( VOAM) aerial video surveys have been carried out in the Brazilian Amazon to provide ground veri cation for mapping of wetland cover with the Global Rain Forest Mapping (GRFM) Project JERS-1 (Japanese Earth Remote Sensing Satellite) mosaics of the Amazon basin. Surveys in 1995 and 1996, acquired with handheld analog camcorders from small aircraft, were timed to imaging of the GRFM low-and high-water mosaics, and limited to within 600 km of Manaus. For the 1997 and 1999 ights, digital camcorder systems were installed in the Bandeirante survey plane operated by Brazil's National Institute for Space Research. The VOAM97 and VOAM99 surveys circumscribed the Brazilian Amazon, documenting ground conditions at resolutions on the order of 1 m (wide-angle format) and 10 cm (zoom format) for wetlands, forests, savannas, and human-impacted areas. Global Positioning System (GPS) information encoded on the video audio track was extracted by mosaicking software that automatically generates geocoded digital mosaics from video clips. On the 1999 survey, a laser altimeter recorded pro les of terrain and vegetation canopy heights. A validation dataset was compiled from the videography for a portion of the GRFM mosaics extending 6°by 4°in longitude and latitude, using randomly selected points along ight lines. Other applications of the VOAM videography include acquisition of ground control points for image geolocation, creation of a high-resolution geocoded mosaic of a forest study area, forest biomass estimation, and rapid assessment of re damage. Geocoded digital videography provides a cost-eVective means of compiling highresolution validation datasets for land cover mapping in remote, cloud-covered regions.*

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Algorithms to calculate chlorophyll (chl) concentrations of phytoplankton were tested over a range from 0.9 to 47 pg chl L-1 in Mono Lake, California. During four surveys on the lake, samples for determination of chlorophyll were collected and continuous spectra from 400 to 800 nm were obtained with a hand-held spectroradiometer. Remote sensing reflectances were calculated from these spectra. The reflectance peak at 689 nm and the reflectance maximum around 689 nm ratioed to the reflectance maximum around 560 nm predicted chlorophyll concentrations well (r2,0.94 for both).