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<br />$6.200 per river km, its high accuracy makes it useful for several monitoring requirements <br />across all GCMRC programs and. therefore. may be quite cost effective. <br /> <br />7. Overall. vertical accuracies from different airborne topographic mapping approaches <br />increase with increasing cost and therefore decreasing surface area Ihat can be mapped. <br />ISTAR automatcd photogrammetry can cover Ihe entire canyon system at 44-cm accuracy <br />for $625/km, manual photogrammetry can map specific areas at 25-30-cm accuracy for <br />$3,000/km. and high-resolution LI DAR can map specific areas at 8-17-cm accuracy for <br />$2.100-$6.200/km. Sediment monitoring will require one of the latter two technologies. <br />whereas system-wide resource monitoring will require the ISTAR system. <br /> <br />4.2.4. Spatial resolution for terrestrial photogrammetry <br /> <br />Stereo image data collections during 2000 included digital panchromatic (18-cm <br />resolution), ClR film (IO-cm resolution), and true-color (6-cm resolution) film. The true-color <br />imagery was scanned at three different resolutions (resulting in 6-. 8-, and 16-cm resolution <br />images) to determine the optimal minimum scan resolution to maintain high vertical accuracy. <br />Photogrammetric analyses of these data were performed by the U.S. Geological Survey and by <br />Pacific Western Technologies (PWT). Our evaluations oflhe resulting photogrammetric <br />elevation data (Davis et aI., 2002b) showed that image resolution needs to be near 6 cm or <br />I :4,OOO-scale photography (Figures 39-40; Davis et aI., 2002b) to produce elevation data with <br />vertical accuracies of25 cm or better, which is the smallest change in sand-bar elevation that is <br />deemed "significant" (Schmidt et aI., 1999). This photographic scale is also the photgrammetric <br />standard scale for meeting a 25-cm accuracy under national map accuracy standards. Digital <br />panchromatic stereo imagery with 18-cm resolution produced very high elevation errors (RMSE <br />= 53 cm; Figure 39; Davis et aI., 2002b), but it is difficult to acquire higher resolution digital data <br />using airborne digital sensors. In addition, the dimensions ofCCD arrays need to be at least <br />10.000 by 10,000 to support accurate photogrammetric analysis. Industry is currently developing <br />such cameras. but it will take a few years for the technology to be proven viable. In the <br />meantime, data to support GCMRC photogrammetric needs will have to be acquired as film, <br />which requires expensive posl-collection scanning and rectificalion if orthorectified imagery is <br />needed. <br /> <br />5.0 Further Evaluations <br /> <br />Although the remote-sensing initiative is officially over, we still need to evaluate some <br />remaining data and new airborne systems to resolve a few remaining issues. <br /> <br />I. DSM data from 1ST A R and the two high-resolution LI DA R data sets need to be <br />reviewed to determine their accuracies in mapping topography within <br />vegetated areas and in mapping canopy volume. <br />2. High-resolution L1DAR should be tested at archaeological sites to determine if <br />this approach can monitor fine-scale morphometric changes in archaeological <br />structures. as well as in arroyos and check dams near such structures. <br />3. GCRMC should proceed to establish a set of fixed, photo-identifiable points <br />within the CRE (with accurate N. E, and elevation values) in order to verify <br />future airborne topographic surveys and to develop a photogrammetric <br />method that is based on these points instead of control panels. <br />4. High-gain, multispectral data of the channel that were collected by Chavez need <br />10 be cvaluated to determine the grain sizes Ihat can be discerned by such <br />imaging systems. <br /> <br />26 <br />