Janette C. Gervin

Direct satellite inference of ecosystem light use efficiency for carbon exchange using MODIS on Terra and Aqua

Understanding the dynamics of the global carbon cycle requires an accurate determination of the spatial and temporal distribution of photosynthetic CO2 uptake by terrestrial vegetation. Optimal photosynthetic function is negatively affected by stress factors that cause down-regulation (i.e., reduced rate of photosynthesis). Present approaches to determine ecosystem carbon exchange rely on meteorological data as inputs to models that predict the relative photosynthetic function in response to environmental conditions inducing stress (e.g., drought, high/low temperatures). This study examines the determination of ecosystem photosynthetic light use efficiency (LUE) from satellite observations, through measurement of vegetation spectral reflectance changes associated with physiologic stress responses exhibited by photosynthetic pigments. This novel approach is now possible because the Moderate-Resolution Spectroradiometer (MODIS) on Aqua and Terra provides frequent, narrow-band measurements of high radiometric accuracy in both the morning and afternoon. Specifically, the reflective ocean MODIS bands were used to calculate the Photochemical Reflectance Index (PRI), an index that is sensitive to reflectance changes near 531 nm associated with vegetation stress responses exhibited by photosynthetic pigments in the xanthophyll cycle. MODIS PRI values were compared with LUE calculated from half hour values of CO2 flux measured at the overpass time at a mature aspen site in the boreal forest of Saskatchewan as part of the Fluxnet-Canada network

Remote sensing of tropospheric chemistry using lidars from geostationary orbit

Tropospheric chemistry is considered to be the next frontier of atmospheric chemistry, and understanding and predicting the global influence of natural and human-induced effects on tropospheric chemistry will be the next challenge for atmospheric research over the foreseeable future. A geostationary Earth orbit (GEO) vantage point provides an ideal location for measuring spatially and temporally resolved distributions of trace gas species. One powerful technique for making this measurement is LIght Detection And Ranging (lidar) using solid-state lasers. Presently, NASA has a notional plan for using lidars for tropospheric chemistry measurements, but from low Earth orbit (LEO). While permitting high spatially resolved measurements, LEO measurements, however, lack the temporal resolution required to monitor important atmospheric processes and transport. A GEO instrument will require a more energetic and efficient lidar system in order to permit accurate measurements. In this study, we investigated the capability of a lidar for tropospheric profiling of chemical species and we develop a roadmap for the requisite technologies.

Identifying roads and houses from scanned aerial photography and combining them with TIGER and digital terrain data of suburban areas

A method for deriving the location of houses and roads from scanned NHAP and NAPP aerial photography using spectral, spatial (spatial smoothing and filtering and road segment size), and contextual (proximity to road) techniques was demonstrated. Despite differences in house size and construction age, analysis of both test and verification sites achieved acceptable accuracies, with more than 92 percent of the houses correctly identified. This house and road image derived from scanned USGS NHAP aerial photography, demographic data from the Bureau of the Census TIGER/Line files, and digital terrain data provided by the USGS Digital Elevation Model (DEM) files were then combined using analysis techniques developed to utilize imagery from spaceborne multispectral instruments.<<ETX>>

Landsat-4 Thematic Mapper (TM) For Cold Environments

The TM aboard Landsat-4 launched on July 16, 1982, represents a major advance in Earth resources sensors. Its seven spectral bands record surface radiation in blue, green, red, near infrared, middle infrared and thermal wavelengths. The spatial resolution of approximately 30 meters represents a sevenfold increase over the previous Landsat sensor, the multispectral scanner subsystem (MSS). In addition, TM has greater radiometric sensitivity, distinguishing 256 quantization levels, compared with 64 for the MSS. These potential improvements have significant implications for satellite remote sensing in cold environments. The addition of the middle infrared bands will permit clouds to be distinguished from snow. It may also be possible to relate spectral response in this range to snow condition and hence water content. The thermal band responds to differences in surface temperature, which may be related to variations in soil moisture and drainage. These are important considerations for cold region construction. Water features, which can be related to circulation and quality, can be detected in the thermal and blue bands as well as the previously available green and red. The finer spatial resolution of TM will permit more accurate location, differentiation and monitoring of the extent and movement of ice and snow. Both spectral and spatial characteristics of TM contribute to more accurate land cover classification and geographical location of individual land cover features. These improved capabilities will make the TM considerably more useful for both civilian and military needs in cold environments.