At a particular altitude, an observer (human eye or electronic detector) perceives the ground according to a cone of visibility depicted in Figure 2.10. Spatial resolution corresponds to the elementary size of the ground surface measured by the different instruments of an embedded sensor. The bottom pattern is the conical scanning footprints. The top two are cross-track patterns with two degrees of overlap. Fig. 15 has FWHM footprints projected on to the surface as examples. Even though the cross track scanner might have a larger swath width, the utility of the most oblique measurements is limited due to the increased spatial resolution. Therefore, the cross track has very unequal spatial resolution across the scan. the along or down track axis) increase as the scan angle increases. For a conical scanner, the major and minor axis of the elliptical footprint stays consistent across the scan, but the cross-track scanner will have the cross-track axis (vs.
The 3-dB footprints can project a circle or more often an ellipse. Spaceborne and airborne measurements quantify the geodetic location of the energy received by projecting the antenna’s FWHM footprint on to the Earth’s surface. This section discusses how we determine the radiation collected and not the accuracy of the geolocation. Spatial resolution (or horizontal cell size) is a measurement’s geographical area on the ground that the upwelling radiation originates from. The temporal resolutions of common sensors are also shown in Table 1.7. The frequency characteristics are determined by the design of the satellite sensor and its orbit pattern. Temporal resolution is a measure of the repeat cycle or frequency with which a sensor revisits the same part of the Earth's surface. Hyperspectral systems usually have hundreds of spectral narrow bands for example, Hyperion on EO-1 satellite has 220 bands at 30-m spatial resolution. Many sensor systems have a panchromatic band, which is one single wide band in the visible spectrum, and multispectral bands in the visible-near-IR or thermal-IR spectrum see ( Table 1.7 ). The spectral resolution describes the number and width of spectral bands in a sensor system.
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