The 68-cm radar echoes from the moon are interpreted with the approximation that the scattering can be described by the laws of geometric optics. The treatment relates the observed angular power spectrum directly with the distribution of surface normals, and no assumed functional dependence of the surface correlation function is required. A simple calculation gives a dielectric constant of 2.6 to 2.8, an average slope of 11 ø to 14 ø, and an rms slope of 15 ø to 23 ø. The depolarization data and the contour of the angular power spectrum are used in selecting these values from the different possible sets. The reduction technique has the added feature that the derived formulas can be used directly to calculate the microwave emissivity as a function of both angle and polarization.
We recently used a geometric optics model to interpret the 68‐cm radar echoes from the moon [Rea et al., 1964]. The angular power spectrum of the radar return was directly related to the distribution function of the surface normals. This in turn was used to calculate the average and rms slopes and the average and rms normals, parameters which can be used to characterize the surface roughness. A comparison of our numbers with those found by other workers using physical optics approaches revealed ours to be somewhat higher than anticipated.
Microwave emissivities have been calculated for a variety of rough surfaces assumed to reflect and emit according to geometric optics. Both the surface dielectric constant and the function defining the distribution of slopes are varied in the calculations. The results are applied to existing passive microwave observations of the moon and Venus. For the moon, the presence of an acceptable roughness can reconcile the dielectric constant calculated from polarimetric data at λ21 cm with the dielectric constant obtained from the λ68‐cm radar data (ε ≃ 2.7). For Venus, the surface parameters obtained from an analysis of the λ12.5‐cm radar results are used to calculate the polarization visibility function. The calculated curve deviates significantly from the curve observed at λ10.6 cm. Because the inclusion of the indicated roughness does not produce a good fit, it is believed that the answer may be found in atmospheric absorption and thermal emission, as suggested by J. E. Hansen and S. Matsushima and by J. V. Evans.
Twito, Roger H.; Mifflin, Ronald W.; McGaughey, Robert J. The MAP program: building the digital terrain model. Gen. Tech. Rep. PNW-GTR-200. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station; 1987. 22 p.PLANS, a software package for integrated timber-harvest planning, uses digital terrain models to provide the topographic data needed to fit harvest and transportation designs to specific terrain. MAP, an integral program in the PLANS package, is used to construct the digital terrain models required by PLANS. MAP establishes digital terrain models using digitizer-traced contour lines from topographic maps, which are, in turn, processed into an elevation grid and stored in matrix form. MAP builds continuous digital terrain models that can cover large planning areas and builds them to any elevation grid spacing desired. Though the MAP method does not always result in digital terrain models that are a perfect equivalent to the topographic map, they should be adequate for planning. A guide giving detailed operating instructions for the programs is included.The MAP program creates the DTMs used by the rest of the PLANS programs. DTMs are created in three basic operations: 1. Establishing the boundary of the DTM. 2. Digitizing the DTM's contour lines. 3. Converting the digitized contour-line data into a DTM. The topographic map of the project planning area is the source from which DTMs are built. The physical size of the topographic map(s) and the resulting DTM coverage area require careful preparation before building the DTM, especially when large areas are being planned for. Usually, large areas have to be subdivided into smaller DTM units. Subdivision is required when: 1. The DTM coverage area is larger than the digitizer tablet, or 2. The DTM coverage area cannot, as a single unit, meet the desired gridline spacing When subdivision is required, the DTM coverage area is divided into equal-size, rectangular DTM units. Later, up to six adjacent DTM units can be loaded and combined into an enlarged DTM when the design programs in PLANS are used.The first step in building a DTM is to delineate the planning area on the topographic map 1/ by carefully enclosing the planning area within a rectangle that defines the DTM coverage area. Next, the user enters the measured dimensions of the rectangle and the desired gridline spacing for the DTM (additional detail on gridline spacing is provided in the appendix), and the program determines if subdivision is required. If subdivision is needed, the program calculates the DTM-unit size necessary to obtain the desired gridline spacing and instructs the user on locating and marking the subdivision boundaries within the DTM coverage area.After the DTM unit is enclosed in a rectangle, elevation data can be entered via the digitizer. First, the location of the DTM unit on the digitizer tablet is established by digitizing the lower left corner of the unit and a point on the lower boundary. Then a process-control menu is taped to the digitizer t...
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