CASPAR Operation and Facilities CASPAR Operation and FacilitiesCASPAR models the performance of airborne, coherent pulse - Doppler, FM and FMCW radar systems operating in a ground clutter environment for monostatic, bistatic and semi-active radar configurations. This involves three principal stages:
The contributions from ground clutter are calculated in terms of the clutter power frequency spectra for a set of radar ranges. For each range, the clutter returns from the set of ambiguous range rings are calculated as a function of look angle, reflectivity and Doppler frequency. These spectra may be used to estimate the obscuration due to clutter in range-velocity space and to calculate the target detection probabilities both for single and multiple PRF's.
Central to the program operating philosophy is the concept of an input data set which resides in program storage during execution and which may be archived to and retrieved from an input data file. CASPAR may be executed in either interactive or batch modes. In interactive mode, the program may be used to perform any of the available program functions, including input data editing, calculations and graphical display. In batch mode, the program operation consists solely of processing an input data file created previously using the interactive mode. However, the data calculated during batch operation may be depicted graphically subsequently by executing the program in interactive mode.
Each set of input parameters is entered via a full screen data editor which provides comprehensive data checking and validation. The input data parameters are grouped into nine data categories:
Facilities are provided for the graphical depiction of the antenna patterns, the receiver pulse weighting function, and the selected clutter model. For the output data, graphical outputs are available for the clutter power spectra, constant clutter contours in range-velocity space, obscuration versus clutter power level, and single and cumulative detection probabilities versus range.
The clutter models are derived from published clutter reflectivity data for various sea states and land types and for frequencies between 1 and 50 GHz. A user defined clutter model may also be specified. The calculation method employs a spherical earth, based upon a 4/3 effective earth radius model to allow for refraction effects, and includes altitude-dependent propagation path loss due to atmospheric absorption. The antenna models are specified in terms of principal plane patterns, which may be defined either in terms of an analytical function with prescribed halfpower beamwidths and first sidelobe levels or user defined models. The Doppler filters are synthesised from one of the standard amplitude weighting functions, including Hamming, Hanning and Taylor, or alternatively, a user specified weighting function may be employed.