Technical Description of the Radar Position Analysis System (RPAS)

Transcription

1 Technology Service Corporation an employee-owned company 55 Corporate Drive 3rd Floor, Trumbull, Connecticut Phone: (203) Fax: (203) Technical Description of the Radar Position Analysis System (RPAS) TSC-RPAS Prepared by: Christopher B. Fish RPAS Program Manager Technology Service Corporation 55 Corporate Drive Trumbull, CT (203)

2 Technical Description of the Radar Position Analysis System (RPAS) Contents 1.0 Executive Summary Technical Description Construction of an Analysis Scenario Performance Analysis Outputs Elevation Database Generation Weapon Characteristics Weapon Trajectory Generation Weapon RCS Data Radar Model Description RPAS System Requirements

3 1.0 Executive Summary RPAS (Radar Position Analysis System) is a position analysis software tool designed to predict the site-specific weapon location performance of U.S. Army Weapon-Locating radars for a wide range of potential weapon placements and characteristics. Given a specific radar position and operational set-up, RPAS estimates the probability of location and location accuracy for any desired weapon firing using the terrain elevation database specific to that site, combined with detailed weapon and radar models. The ability to estimate performance is particularly important whenever there is any significant variation in the terrain elevation in the region of interest because of the restrictions imposed on the useable elevation coverage provided by the radar. RPAS predicts how the radar will perform in these scenarios before the radar is in position and in operation. It is automated and easy to use and is the most comprehensive siting tool available to the Army and Marines. The benefits of using RPAS include: Feasibility determination of any site selection Siting optimization of the U.S. Army Weapon-Locating radars Performance optimization of the U.S. Army Weapon-Locating radars Rapid assessment of alternative radar sites More comprehensive than manual analyses Provides insight into operational problems in the field Builds user experience/confidence in radar site selection Provides the user confidence in successful mission accomplishment Compatible with other radar systems TSC delivered the first RPAS in the spring of 1996 in response to a request from the U.S. Army. Since that time, the product has been refined and upgraded with several new features added. Many RPAS units have now been supplied to the U.S. Army and the U.S. Marine Corps. RPAS is currently used as a training aid at the U.S. Army Field Artillery School at Ft. Sill, Oklahoma. In addition, RPAS supports U.S. troops at military bases and facilities worldwide, including South Korea, Bosnia, Germany, Afghanistan and Iraq. The original RPAS units were configured as computer workstations. RPAS is currently being supplied for use on desktop and laptop personal computers running Microsoft Windows, Redhat Linux, or the Solaris Operating System. The current RPAS configuration provides a wide range of options and capabilities for performing weapon location analyses. Important options and features include: All U.S. Army Weapon-Locating radar types RPAS provides models for the LCMR (V)2, AN/TPQ-36(v)7, AN/TPQ-36(v)8, and AN/TPQ-37 FIREFINDER radars. In addition, models can be created for other radar types allowing RPAS to be used with other systems. 3

4 Extensive weapon capabilities RPAS generates realistic weapon trajectories for mortars, artillery and rockets between user-defined launch and impact locations. Three subcategories of weapons are available in each weapon family. In addition to the default weapon definitions provided, RPAS also provides the capability to define new weapon trajectory or radar cross-section characteristics. Extensive assessment capabilities Probability of location, location accuracy and radar specification requirements are provided for each weapon firing in the hostile mode of operation. Point-to-point, area-to-area, single-weapon, multiple-weapon and volley fire analyses can be conducted. Radar Network assessment capabilities The operator has the ability to site, analyze and display a network of up to seven radars. Meaningful output data Graphical outputs provided by RPAS allow the user to understand the radar performance and siting issues at the site being analyzed. Terrain height, screen angle, elevation coverage, clutter intensity, terrain visibility, and target-tointerference ratio plots are available. Optimized human interface RPAS facilitates operation by providing user-friendly menus for data entry and file management. Radar parameter optimization By varying the available radar settings such as elevation coverage (for all radar types) or video integration (for the AN/TPQ-36 only), radar performance and parameters can be optimized. Simplified DTED database creation RPAS provides for the construction of elevation databases and libraries in a straightforward manner. Consistency/repeatability The RPAS software is consistent in its approach to each weapon location analysis and performance estimates are repeatable. The U.S. Army is now offering RPAS to foreign military customers of new U.S. Army Weapon-Locating radars as part of the standard equipment package. RPAS was also used as a validation tool by the U.S. Marine Corps in a study aimed at extending the operating range of the AN/TPQ-46A radar. One highly satisfied RPAS user, a U.S. Army Sergeant, called TSC on his safe return from Iraq to let us know that RPAS had been a true force multiplier. More recently, Army Chief Warrant Officer Three Michael Harp, now stationed at the National Training Center, reported to TSC that his radar team had achieved a 96 percent acquisition rate while stationed in Iraq no doubt because we used RPAS. CW3 Harp wrote-up RPAS in an article published in the September-October 2005 issue of Field Artillery Magazine titled Counterstrike at the NTC Reversing Negative Trends. In early 2003, TSC conducted a study, using RPAS, to quantify the increased range performance that might result in the AN/TPQ-36(v)8 radar as a result of improvements to receiver output signal-to-noise (SNR). Initially, TSC determined the performance range limit for the current system by evaluating the probability of location of an in-bound medium-range rocket, 4

5 which had been identified as the weapon of interest. TSC then studied the potential range performance improvements that would be yielded by incremental increases in receiver SNR. The performance of the radar against medium artillery was also studied. In a follow-up to this study, the RPAS software was used to identify the parameters that impact the radar performance at extended range and to determine the optimum values to maximize the extended weapon location range of the radar. TSC also used RPAS to support a Counter Mortar/Rocket Force-On-Force Engagement study that included the modeling and simulation of AN/TPQ-36 and AN/TPQ-37 FIREFINDER Radars. TSC continues to provide support and consultation to the U.S. Army in matters related to the radars as modeled in RPAS as well as in the development of specific and non-standard weapon (mortars, artillery, rockets) models for use in the RPAS software tool. TSC has sold RPAS licenses to a number of NATO countries through the Army s Foreign Military Sales program and we provide operator training and maintenance support to these customers. 2.0 Technical Description The Radar Position Analysis System can be described as an integration of three basic building blocks that are used to perform an analysis of a weapon-locating radar s position. These building blocks are a terrain elevation database, a model of the weapon-locating radar s characteristics and a weapon model. These basic building blocks are shown in the RPAS block diagram of Figure 1. The terrain elevation database should cover the region including the radar Weapon Trajectory Characteristics Weapon RCS Characteristics Terrain Elevation Database Radar Position Analysis Radar Models Probability of Location and Location Accuracy Estimates RPAS Graphical Outputs Figure 1. RPAS Block Diagram 5

6 positions and the weapon launch and impact locations. After initialization, the weapon-locating radar is characterized by multiple radar mode operation. A weapon model consists of both trajectory and radar cross-section (RCS) characteristics. The key RPAS outputs for any position analysis include the probability of location and location accuracy for any weapon firing. Other outputs that are available include various graphical data that provide the user with a wide range of information relating to the scenario under evaluation and the suitability of the site or operational parameters selected. RPAS operational procedures and the nature of the various performance analysis outputs that are available are summarized in the following subsections. Basic RPAS operation includes the construction of an analysis scenario, elevation database generation and weapon trajectory generation. Also discussed are the operational aspects of entering new weapon data. More detailed explanations of the step-by-step processes are provided in an operator's manual that will be supplied with any purchase of RPAS. A description of the radar models used to describe the search, verification, tracking and location modes of the weapon-locating radars is also provided. 2.1 Construction of an Analysis Scenario The construction of an analysis scenario is accomplished in RPAS through a five step process that includes the selection of a radar configuration, the selection of a terrain database, the specification of radar location, the setting of the radar search fence, and the specification of weapon trajectories. Following these five procedures, a performance analysis can be conducted. The process begins with the selection of a radar set from the list of LCMR, AN/TPQ-36 and AN/TPQ-37 variants that are available. The second step is the selection of the terrain database from those that have been previously generated and stored. The straightforward method used for database generation is described in Section 2.3 that follows. The third step requires that the Easting and Northing values of the radar position be entered as well as the appropriate UTM zone. The local datum can also be selected from a list of stored datums. The fourth step of setting the search fence is crucial to the performance analysis and closely follows actual radar initialization procedures. The search fence menu for the FIREFINDER radars is shown in Figure 2a, and the sector setup menus for the LCMR radars are shown in Figures 2b and c. For the FIREFINDER radars, the RPAS user enters the platform height adjustment, antenna azimuth, frequency limits, sector edges and minimum and maximum sector ranges for the radar in use. The terrain in the database is then surveyed to determine the appropriate elevation angles over the azimuth sector. A manual terrain mask capability allows the modification of this mask or the creation of an entirely different set of mask angles. The minimum screen angle of in-sector terrain can then be entered or the standard default value selected. Finally, a flat mask or a terrain following search fence can be selected to complete the search fence set-up procedure. Additionally, for the AN/TPQ-36 radar, video integration can be set to ON or OFF. For the LCMR radar, the RPAS user enters the platform height adjustment, the radar transmit frequency, and the antenna boresight angle from true north in the Sector Settings Menu and additionally selects the active beams in the Transmit Sector Menu. 6

7 Figure 2a. RPAS FIREFINDER Search Fence Menu Figure 2b. RPAS LCMR Sector Settings Menu Figure 2c. RPAS LCMR Transmit Sector Menu The fifth and final step of scenario construction is the specification of weapon trajectories for the different hostile weapon location options that are available in RPAS. For single weapons, a point-to-point or area-to-area analysis can be conducted. In the standard point-to-point analysis, launch and impact points are entered for any weapon of interest. In the area-to area analysis, four-sided convex areas can be entered for the launch and impact locations and the analysis will 7

8 proceed with a low, medium or high resolution division of these areas. Point-to-area and area-topoint analyses can also be conducted. There is also a multiple weapon capability within RPAS. This is performed only for point-to-point trajectories. Up to five different weapons can be launched simultaneously with distinct launch and impact locations, and the performance analysis will be conducted and reported for each weapon. Additionally, a volley fire analysis can also be conducted. This can be done for from 3 to 6 weapons in a battery with a uniform spread in firing times over a 2 second period. The individual weapon launch points are distributed laterally or circularly over a distance controlled by user input. The basic procedure for generating the proper weapon trajectories is described in Section that follows. Following the procedures outlined in this section for the construction of an analysis scenario, performance analysis outputs are generated for all the weapons being analyzed for hostile mode location. 2.2 Performance Analysis Outputs The RPAS graphical outputs present a wide range of information to allow the user to make a proper assessment of the site being analyzed. Terrain height, screen angle (terrain elevation angle), elevation coverage, clutter intensity, terrain visibility, and target-to-interference ratio plots are all available. While the plots show different data in a variety of formats, there are several features that are common to all the RPAS plots. These include the ability to zoom and pan to any area for more detail, to extract certain statistics by clicking on a point of interest, to save the plots for future examination and to make a hardcopy for reference. weapon-locating radar positions and weapon launch and impact locations are indicated on all graphical outputs. Additionally, a performance spreadsheet provides the critical information relating to the various weapon analyses conducted. The key performance estimates of probability of location and location accuracy obtained by RPAS are reported on the spreadsheet as well as on various graphical outputs. In addition to the performance estimate values, a condition color is also provided to allow the user to make a rapid assessment of the performance obtained. The condition color compares the estimated performance determined by RPAS with the actual radar s specified performance. Condition GREEN is reported if the probability of location and location accuracy performance estimates obtained for any analysis are as good as or better than the specification requirements. Condition YELLOW is reported if the estimated performance does not quite meet the specified levels. Condition RED is reported if the estimated performance is significantly worse than the specification requirements. A condition BLACK is also reported whenever no weapon locations were obtained for a particular analysis. As one of the graphical outputs, the RPAS Terrain Plot provides the operator with colorcoded topographic information for the region of interest. The terrain height is indicated by the color code. A typical RPAS Terrain Plot is shown in Figure 3. with a single weapon trajectory 8

9 Figure 3. RPAS Terrain Plot Figure 4. RPAS Screen Angle Plot 9

10 overlaid. The visualization of the terrain provided in this plot allows the operator to construct the proper scenarios for evaluation. The RPAS Screen Angle Plot provides a display of the screening that is caused by the terrain surrounding the radar. The plot shows the terrain elevation angles as a function of azimuth angle, with the range of the terrain indicated by the color code. A typical RPAS Screen Angle Plot is shown in Figure 4. with two weapon trajectories overlaid. This plot is generally the most useful graphical representation of the weapon location problem being analyzed because the perspective provides both the terrain and weapon elevations as seen by the radar. The plot also shows the search fence setting as well as the maximum and minimum beam elevations. This helps the user understand the elevation coverage issues in the azimuth sector of interest by illustrating the track volume that exists above the search fence. The RPAS Elevation Plot provides the operator with an assessment of the elevation coverage in easily understood green/yellow/red/black color code. The green color indicates those azimuth regions where more than two-thirds of the radar s elevation coverage is available for target detection and tracking purposes. The yellow color is used for between one-third and twothirds, and red is used for less than one-third. Black is used to indicate no coverage. Within the sector of interest, green and yellow colors are preferred to red and black. A typical RPAS Elevation Plot is shown in Figure 5. The plot is always generated for a full 360 degrees of azimuth, regardless of the specified azimuth sector of interest. The RPAS Clutter Plot indicates regions where strong competing ground clutter may reduce the radar s performance especially for targets with low radial velocities. The color code indicates the clutter-to-noise ratio (CNR) values in decibels (db). A zoomed version of a typical RPAS Clutter Plot is shown in Figure 6. When applicable, if the search fence is properly set, radar performance is highly insensitive to the presence of ground clutter. Search beams placed too low in elevation, however, will raise the CNR levels significantly and degradations in radar performance may occur if there is a ground clutter return present with the target return. The RPAS Visibility Plot shows how high above the ground an object must be in order to be visible to the weapon-locating radar. Visible ground is colored white, with a color code used for the remaining height information. A typical RPAS Visibility Plot is shown in Figure 7. This information can also be used to determine the visibility of the weapon-locating radar. The RPAS Trajectory Target-to-Interference Ratio (TIR) Plot provides the operator with an understanding of the quality of the radar data that the weapon-locating radar will provide for a particular weapon firing. The TIRs are shown along the tracked portion of the trajectory and the higher the TIR the higher the probability and accuracy of weapon location. If TIR ratios less than 20 db are indicated, this may be the cause of low probabilities of location or inaccurate locations. A zoomed version of a typical RPAS Trajectory TIR Plot is shown in Figure 8 and corresponds to the RPAS Screen Angle Plot shown in Figure 4. The performance spreadsheet that is provided in addition to the graphical outputs allows the operator to view a printed history of a site analysis. The spreadsheet contains the date and time of the analysis, the radar parameter file used in the analysis, the radar in local datum and WGS-84 coordinates, the search sector parameters, and the weapon trajectory and performance data for every trajectory analyzed. 10

11 Figure 5. RPAS Elevation Plot Figure 6. RPAS Clutter Plot 11

12 Figure 7. RPAS Visibility Plot Figure 8. RPAS Trajectory TIR Plot 12

13 2.3 Elevation Database Generation Elevation database generation is a self-contained feature of RPAS and runs from a single menu activated by the Elevation Database button on the main RPAS application bar. A CD- ROM with DTED data is inserted into the drive and initialized with a single click procedure. The center of the area stored on the CD is reported to the user who can then specify his own map center coordinates. The user also specifies his map extent and resolution and names the map to be created. The software will prompt the user if additional CDs are required to complete the map specified. As many as four separate CD-ROMs can be used to create a single database. A library of databases can be generated and stored through the continued use of the database generation tool just described. The current RPAS configuration is compatible with DTED Level I and II available from the U.S. National Imagery and Mapping Agency (NIMA). NIMA data is not provided by TSC. Other DTED data matching the NIMA DTED data format can also be used within RPAS. Alternate data sources for DTED data have been identified by TSC and this option can be discussed if necessary. 2.4 Weapon Characteristics The weapon families that can be analyzed in RPAS consist of mortar, artillery and rockets. Within each of these families, three subcategories of weapons are available. For mortars and artillery, there are light, medium and heavy designations. These designations are based on the diameter of the weapon. For rockets, there are short range, medium range and long range designations which are designed to have maximum ranges of 15, 30 and 60 km, respectively. In general, each weapon is described by its trajectory generation parameters, radar cross-section (RCS) data and length Weapon Trajectory Generation Weapon trajectory generation in RPAS is based on the launch and impact positions entered by the user and the drag characteristic and atmospheric data stored within RPAS. A point mass model is assumed and drag coefficient data is stored as a function of weapon speed. For mortars, the initial trajectory solution offered assumes an 800 mil quadrant elevation (QE) angle and solves for the launch velocity. The user can change the displayed values of initial weapon velocity or QE as desired and another mortar trajectory will be generated. For artillery shells, the initial trajectory solution assumes the stored maximum weapon velocity and solves for the lowest QE possible. The user can again change the displayed values to generate another artillery shell trajectory. For rockets, nominal burn times, mass fractions and initial accelerations are stored for each of the three rocket types. For this weapon, the range of the weapon determines the QE value at launch that is reported to the user. In addition to the baseline trajectory capability just described, new weapon trajectories can also be generated. In the case of mortars and artillery, weapon range, initial velocity and drag characteristic can all be modified. Modification of any two of these parameters, will provide a solution for the third. The newly defined weapon can then be stored for subsequent use. In the case of rockets, various combinations of weapon range, burn time, burnout velocity and drag characteristic can be modified. Solutions for range, burnout velocity and drag are then provided 13

14 and can be stored as a new weapon file. Whenever drag is modified, the stored drag characteristic is scaled by the same multiplicative factor for all weapon speeds. The weapon trajectory capability offered provides a broad range of characteristics that will suit the needs of the user performing radar position analysis. The new weapon definition menu which is used for the adjustment of trajectory parameters, RCS data and weapon length is shown in Figure Weapon RCS Data Figure 9. RPAS New Weapon Definition Menu For each of the nine different weapon types available in RPAS, single-valued, non-aspect angle dependent values of RCS are stored and can be used during any position analysis. The user also has the ability to modify these values and create new weapon RCS definitions as needed. This can be done in several ways. First, the single RCS value stored for any weapon type can be changed to another value and stored in a new weapon file. Additionally, aspect angle dependent RCS values can also be entered. This can be done by manual data entry or by reading data from a floppy disk with a simple data format requirement. The finest resolution of data allowed is 1 degree for the 180 degree range of aspect angle. In addition, if both components of RCS data are 14

15 available from vertical and horizontal polarization measurements, they can also be entered. The new weapons that are defined can be stored and used in any subsequent analysis. 2.5 Radar Model Description The radar models in RPAS accurately reproduce the search, verification, tracking and location mode performance of the actual weapon-locating radars. Upon request, TSC will provide estimates for the development of models for other radar types to expand applicability to other systems. The basic RPAS model is a beam dwell by beam dwell simulation that uses analytical equations, such as the radar range equation, to describe radar operation. A wide range of parameters that describe the weapon-locating radar systems are utilized. The front-end parameters include peak power, radio frequency, antenna gain, antenna patterns, system noise temperature and system losses. The waveform and signal processing parameters include the pulsewidth, pulse repetition frequency, integration length, Doppler filtering characteristics and detection thresholds. Additional parameters, among others, include system latencies, track rates, beam-splitting constants, system random and bias errors, and various in-track and end-of-track discriminant settings. Each of the different weapon-locating radars is uniquely modeled and all the significant differences between the radars are taken into account. This would include, for example, the use of frequency steering in elevation for the AN/TPQ-36 radar, which provides only discrete changes in elevation pointing, as compared to phase steering in elevation for the AN/TPQ-37 radar, which provides continuous changes in elevation pointing, and track-whilescan operation of the LCMR radars. The search mode model in RPAS uses the search fence established during scenario construction and consists of a series of simulated beam dwells that emulate the specific beam placement and waveform sequences used in the radar. The weapon launch time is distributed uniformly random over the search scan period to develop the proper statistical variation in the radar performance measures. The radar range equation is used for each dwell of interest and weapon detectability is determined from the standard Swerling detection models used in radar analysis. Weapon position, velocity and radar cross-section characteristics are all included in the approach. Throughout the search, verification and tracking modes of the radar, the target line-ofsight visibility from the radar is determined from the elevation database that is in use. Ground clutter is included in RPAS by calculating the signal return from all visible terrain weighted by the antenna pattern characteristics of the radar. Other forms of clutter, such as the signal returns from rain or birds, are not currently modeled in RPAS. In addition, the growth in the scan period of the search mode is modeled when weapons are being tracked during any multiple weapon analysis. The FIREFINDER verification mode model in RPAS is used to confirm any search detection. Successful verification leads to the start of tracking. Otherwise, the search mode is allowed to continue. The FIREFINDER tracking mode model in RPAS consists of a series of simulated beam dwells that are placed on the target at the prescribed update rate. For the AN/TPQ-37 radar, a single dwell process using monopulse angle measurements is modeled. For the AN/TPQ-36 radars, a four-beam track cluster process using sequential lobing for angle measurement is modeled. Track discriminant data is used as necessary over the track history. A target that is 15

16 dropped from the track mode can be reacquired in the search mode as long as it is in the field of view. The location mode model in RPAS uses the data that is generated during the tracking, or track-while-scan, mode to form an estimate of the location accuracy of each weapon location. The range, azimuth and elevation measurement inaccuracies that are generated over the track history are used to create a range and cross-range error for each trial. Each weapon location analysis consists of 1000 independent trials. The location accuracy that is reported is the circular error probability (CEP), which is the median value of miss distances reported. The probability of location that is reported is the percentage of the weapon locations that occur due to a successful progression through the search, verification, tracking and location modes of the radar out of the 1000 trials conducted. 3.0 RPAS System Requirements RPAS is available in packages configured to run on both the Microsoft Windows Operating System, using the Cygwin operating environment or the Redhat Enterprise Linux Operating System. Versions configured to run under the Solaris Operating System on an Intelbased PC platform are available upon request. Below are the system requirements for Microsoft Windows Operating Systems. PC Platform Minimum Requirements: Operating System: Windows XP, Vista, or Windows 7, Redhat Enterprise Linux 5, Solaris 2.5 or higher CPU: 90 MHz Pentium RAM: 48 MB HDD: 2 Gigabyte Display: 16 color VGA Plus: CD-ROM The installation and set-up procedures for both the hardware and software components are described in detail in an operator s manual that will be supplied with any purchase of RPAS. 16