Synthesised radar aperture eclipsing and nadir return graphs in MATLAB
Scientific Research Institute of Precision Instruments, 51, Str., Dekabristov, Moscow, 127490, Russia
This paper discusses the calculation method of spaceborne synthesised aperture radar (SAR) eclipsing and nadir return graphs in MATLAB. Spaceborne SAR systems operate in conditions of effect of blind zones and nadir returns presence. The correct selection of the period of repetition frequency of the probing signal allows reduce the effect of these factors on the echo-signal. However, distribution of these factors depends on slant range and spacecraft orbit height. Theses parameters, in turn, depend on the height of the terrain.
The paper presents geometric relationships of SAR side view including orbit high changes and height of the terrain. Signal timings of probe, echo and nadir signals are set out. Eclipsing and nadir return graphs are calculated and built using MATLAB functions. Graphs were plotted as functions of slant range and repetition period.
The effect of terrain and elevation changes of the orbit of the spacecraft on the position of eclipsing and nadir returns zones on graph were studied. Linear dependence between slant range and repetition period for boarders of eclipsing and nadir returns zones was found. An analytical dependence between number of eclipsing and nadir returns and their positions on graph was established. The results of graphs calculations in MATLAB and using analytical dependences completely coincide.
Thus, presented analytical dependences help to calculate positions of eclipsing and nadir return zones on graphs much easier and quickly. For example, these analytical dependences can be used to produce an on board algorithm of spaceborne SAR probe signal repetition period calculation.
Keywords:synthesised aperture radar, blind zones, nadir returns
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