![]() 16.6C), one can see well-marked boundaries of relatively large craters.Ĭatchment area measures an upslope area potentially drained through a given point on the topographic surface ( Table 2.1). Artemis Chasma (30°–45°S 120°–145☎) and some other surface features are pronounced on the k v map of Venus ( Fig. Among other features, the k v map of Earth shows “mega-scarps”, such as edges of continents and mountains ( Fig. Vertical curvature is a measure of relative acceleration and deceleration of flows (positive and negative values, respectively). ![]() 16.5C) resulting from a predominance of craters at the global scale. For the moon, the horizontal curvature represents cell-like patterns ( Fig. For example, one can see them on Beta Regio slopes (15°–45°N 270°–300☎). On Venus, flow structures appear slightly at the global scale ( Fig. ![]() There is a system of flow structures incoming to Utopia Planitia from Nilosyrtis and Protonilus Mensae and Elysium Planitia and Mons (5°–70°N 75°–150☎). 16.5A), one can see flow structures, probably of lava origin, beginning on slopes of Alba Patera and forming a huge fan in the North Polar Basin (30°–75°N 200°–310☎). For Earth, they are most pronounced in ocean basins ( Fig. These areas relate to spurs of valleys and ridges (blue and yellow patterns on the k h maps, respectively), which form so-called flow structures. Horizontal curvature delineates areas of flow divergence and convergence (positive and negative values, respectively). Global maps of morphometric variables represent peculiarities of megatopography in different ways, according to the physical and mathematical sense of a particular variable. For example, a Venus map at the scale 1:1,000,000 approximately corresponds to a Mars map at the scale of 1:500,000 and a moon map at the scale 1:250,000. It is recommended to use the same angular resolution in comparative cartographic analysis of different-sized planetary bodies: the ratio of map scales of planetary bodies should be equal to the ratio of their sizes ( Burba, 1984). Florinsky, in Digital Terrain Analysis in Soil Science and Geology (Second Edition), 2016 16.3.1 General Interpretationįor the same angular resolution of 30′, DTMs and morphometric maps of Earth, Mars, Venus, and the moon have distinct linear resolution (around 55.2 km, 29.5 km, 52.8 km, and 15.2 km on the equator, correspondingly) and scales. The general procedures of such processing are reviewed in the usual radio astronomy textbooks. This can be improved by a deconvolution procedure, using either the CLEAN or maximum entropy method (MEM). Such an image often has strong side lobes. However, usually a good image of the sky can still be obtained, thanks to the sparse nature of sky source distributions. Because each ( u, v) point corresponds to one Fourier mode of intensity distribution, the missing modes cannot be reconstructed accurately. In such an array, the sampling on the uv plane is also sparse. This procedure is called “gridding.” In many interferometer arrays, the antenna distribution is sparse and the spacing between the antennas is far larger than the size of the antenna, so that the geometric area of the array is far larger than the collecting area. Of course, in reality the array baselines can only sample part of the ( u, v) space, so one has to make interpolations from the measurement to obtain the visibility at regular grids. The above is then reduced to a two-dimensional Fourier transform, and can be easily inverted as efficiently as an inverse two-dimensional Fourier transform. With small angle approximation, the w-term can be neglected. V ij = ∫ dl dm 1 − l 2 − m 2 A ij l m T l m e − i 2 π ul + vm + w 1 − l 2 − m 2 − 1
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