Advanced Low Altitude Radar Model

ALARM is a generic digital computer simulation designed to evaluate the performance of a ground-based radar system attempting to detect low-altitude aircraft. The purpose of ALARM is to provide a radar analyst with a software simulation tool to evaluate the detection performance of a ground-based radar system against the target of interest in a realistic environment. The model can simulate pulsed/Moving Target Indicator (MTI), and Pulse Doppler (PD) type radar systems and has a limited capability to model Continuous Wave (CW) radar. Radar detection calculations are based on the Signal-to-Noise (S/N) radar range equations commonly used in radar analysis. ALARM has four simulation modes: Flight Path Analysis (FPA) mode, Horizontal Detection Contour (HDC) mode, Vertical Coverage Envelope (VCE) mode, and Vertical Detection Contour (VDC) mode.

The primary application of ALARM is the evaluation of target detection range as a function of the environment. The model now includes the environmental effects of atmosphere, terrain masking, clutter, multipath, and electromagnetic propagation through the use of Joint Aircraft Survivability Program Common Modeling Component Set (JASP CMCS). Land clutter reflectivity probability distributions published by Massachusetts Institute of Technology (MIT) Lincoln Laboratory and sea clutter reflectivity probability distribution from the Center for Naval Analysis (CNA) are also used in ALARM. Pattern propagation effects such as radar antenna pattern, spherical earth and knife edge diffraction, and multipath are included by use of the MIT Lincoln Labs Spherical Earth/Knife Edge (SEKE) Diffraction source code. Terrain masking is determined based on National Geospatial Intelligence Agency (NGA) Digital Terrain Elevation Data (DTED), data input into the model for a specific radar site area. Additionally, ALARM supports limited modeling of onboard noise (self-screening) jammers, onboard deception (coherent) jammers, and standoff noise jammers.


The input consists of user-supplied, engineering-level data, such as transmitter power, pulse width, pulse repetition frequency, antenna patterns, radar cross section (RCS) tables, and data needed to simulate pulsed/MTI, and PD processing. FPA mode requires aircraft flight data parameters to be specified for each data point. These parameters include altitude, heading, speed, bank, and pitch. Alternatively, the FPA mode can read a BlueMax output file for the flight path data. HDC mode requires a single aircraft speed and altitude. VDC mode only requires a single aircraft speed. Data sets for threat systems are available.


The output consists of an output file and a data diary file. The output file is an ASCII text file that includes a summary of the simulation inputs. For FPA mode, the output file also contains the target flight path information summary, which gives detailed information for the target, jammers, target masking, and radar detection at each target location. The data diary file contains the simulation results. Each simulation mode has its own data diary format. The data diary can be in ASCII or binary. The supporting post-processing programs use the data diaries for generating plots.

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DISTRIBUTION STATEMENT D.Distribution authorized to the Department of Defense and U.S. DoD contractors only, CRITICAL TECHNOLOGY, July 2006. Other requests for this document shall be referred to AFRL/IFSD, Wright-Patterson Air Force Base, Ohio 45433-7334.

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