Requirements for ground-, aerial-, and satellite-based remote sensing, image processing, and classification techniques for surveys of the Colorado River delta.

   Biological diversity is the variety and variability among living organisms and the environments in which they occur; it is recognized at genetic, species, ecosystem, and often landscape levels of organization. Biodiversity is linked to the persistent health and vigor of the biosphere, so that biodiversity is not only recognized as an indicator of the condition of the global environment, but also as a regulator of ecosystem functioning (Solbrig, 1991). A common goal of the researchers in the delta area is to interpret the spatial patterns of vegetation communities and their relationship to broad ecological patterns. Scale is an important feature of biodiversity and how species richness can be measured in complex ecosystems. A continuum of species richness exists across broad geographic gradients, along environmental gradients between communities within a landscape, and between micro gradients or pattern diversity that measures the change in composition between points within a community (Whittaker, 1977). Remote sensing and field census are the basic methods to collect, model, and map species richness across this array of ecological dimensions.

Issues and concerns with remote sensing measurements, classification of riparian habitat, and image processing

   The issues related to using remote sensing techniques to measure and map riparian habitat, concerns with having a common system for land cover classification, and probles wth aerial-image processing (georectification, georeferencing, and mosaicking) are discussed. First, ground-work to collect biological data on the Colorado River delta is certainly time-consuming and difficult; remote sensing tools can provide broader coverage in a more timely, accurate manner. However, ground studies are still needed, and in the desert, these are difficult due to the vastness of the area, the severe climate and the lack of roads. U.S. scientists do not have routine access to the study area, but the entire ecoregion is dependent on flows of water released from the United States to Mexico. It is important that both nations have a common database from which to work, as one of the main problems has been matching differently scaled, transborder map data.

   Remote sensing methods could be used to resolve some of the technical issues surrounding the delta so that all sides at least have a common database from which each information layer is available from a GIS. The next problem to be addressed is that people do not necessarily agree on the landscape classifications, as it is a continuum of vegetation types and ecological communities that is arbitrarily divided by people with opposing perspectives. Finding a uniform method of mapping the vegetation in the biome such that descriptions and what was measured in each classification fit the overall purpose for each interested party.

   Aerial surveys of the delta have been somewhat problematic in that critical target areas have been missed (plane not over the target), sensors have failed (the high temperatures in the plane have caused shorts in the equipment), images are difficult or impossible to georeference (not flying flat (pitch, roll) or north (off-transect) or the tilting of plane has caused distortion in the images), and thus, the quality of the georectification and mosaicking of the images is decreased.