Environmental Engineering Reference
In-Depth Information
Airborne Imagery (Aerial Photography)
High-altitude stereo-aerial photographs
provide the smallest scale images for stereo-
viewing, ranging in scale from 1:125,000 to 1:100,000, yielding substantial detail
on terrain features (
Figure 2.7)
.
Worldwide coverage, including the United States,
is spotty.
●
Stereo pairs of aerial photographs
provide the basis for detailed engineering geologic
mapping. They can be obtained in panchromatic, true color, or color infrared
(CIR). Single photos in true color and CIR are given in
Figure 2.8.
Detailed stud-
ies of large to small areas should be based on stereoscopic interpretation. Because
aerial photographs are the basis for modern topographic mapping they are avail-
able on a worldwide basis, at least at scales of 1:50,000.
●
Hyperspectral Imagery
Multispectral scanners discussed above obtain images over a small number of broad spectral
bands of the electromagnetic spectrum. They lack sufficient spectral resolution for precise
surface studies. Hyperspectral imaging (imagery spectrometry) has been developed in recent
years to acquire spectral data over hundreds of narrow, descrete, contiguous spectral bands.
Various systems include SIS, AIS, AVIRIS, HIRIS and HYDICE, and others. Some are carried
by satellite (HIRIS), while others, such as AVIRIS (Airborne Visible/Infrared Imaging
Spectrometer), are flown on aircraft platforms at heights of up to 100 km above sea level.
The main objective of AVIRIS is to identify, measure, and monitor constituents of the
Earth's surface based on molecular absorption and particle scattering signatures. Some
applications include mineral identification for the mining industry for new sites and for
mine waste studies (Henderson III, 2000).
Sheet wash of
Bajadas
Catalina Mts.
See
Fig. 7.30
Fan
Fine-grained
valley soils
FIGURE 2.7
NASA high-altitude stereo-pair of an area northwest of Tucson, Arizona (scale 1:125,000). Apparent are sheet
wash and sheet erosion of the “bajadas” alluvial fans of granular soils, valley fill of fine-grained soils, and the
“dry wash” of the Santa Cruz River, all typical depositional forms in valleys adjacent to mountains in arid to
semiarid climates.The blocked area is shown at a larger scale on a stereo-pair in Figure 7.30. (Original image by
NASA reproduction by US Geological Survey. EROS Data Center.)
