INTRODUCTION - EPS-M SERIES DESCRIPTION
The EPS M Series scanning spectrometer is based on modular components developed for the EPS (Environmental Probe System) and DAIS (Digital Airborne Imaging System) families of airborne imaging spectrometers such as the EPS A Series, EPS H Series, DAIS 3715, DAIS 7915 and the DAIS 2815. The EPS M Series operates on a 16 bit dynamic range and provides multiple spectral data channels with one additional housekeeping data channel. The number, placement and bandwidth of these channels are determined by the customer's application requirements. This is accomplished by using one flexible, grating based spectrometer module for the 01.0µ region. A bandpass filter-based module is used to provide a thermal band typically covering the 8.0 to 12.0 micron range, thermal band. Many of these modular components are field upgradable. The data are recorded by an on-board Exabyte Mammoth or other compatible Small Computer System Interface (SCSI). The system uses an intelligent VME interface based controller incorporating an imbedded Sun compatible workstation. The extended HyperView™ real time operating system (GER proprietary and derivations of GER intellectual property) provides comprehensive system control functions as well as "real-time" data monitoring is including GPS and other navigational. A single-axis gyro mounted on the scan head for measuring roll of the system in operation is a standard system feature with a three axis as an option. Gyroscopic correction information is used for real-time image correction for roll and is also recorded on the housekeeping channel with other system parameters for multi-axis correction. Unlike other scanners whose scan speeds are incremental, the GER systems provide continuously variable scan speeds. A scan frequency as low as 2 Hz can be achieved. The maximum scan speed is limited primarily by the data flow rate of the recording media. The EPS A Series using an EXABYTE Mammoth recorder provides scan speeds up to 100 scans per second. System specifications are summarized in Appendix.
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Scanner Module - Kennedy Scanner
The Kennedy scanner is a multi-faceted optical scanner. The Kennedy scanner splits the optical field into two paths and focuses them coincidentally at the entrance to the spectrometer, i.e., two images collected from infinite object space co-registered and perfectly aligned at the spectrometer's entrance aperture in total reinforcement of each other. This configuration offers a large effective collection aperture with high scan efficiency (duty cycle) in a compact configuration. Optional temperature controlled blackbodies are available to provide a calibrated thermal reference at the beginning and end of each scan line.
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The figure below illustrates the basic optical configuration of the Kennedy scanner. The rotating polygonal mirror changes the direction of view and provides four scan cycles per mirror revolution. T4he focal length of the parabolic focusing mirror is 4 inches. The system is designed for perfect co-registration and focus at infinity.
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The scanning polygonal mirror is driven by a DC servomotor and is controlled using a digital rotary encoder. Both the speed and absolute position of the polygonal mirror are controlled using an intelligent controller that provides high accuracy in controlling scan properties. Encoder measurement of position is also used in conjunction with the roll gyro to provide real-time compensation for aircraft roll.
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The imaging spectrometer provides multiple channels of spectral information. Unlike other commercial imaging spectrometers, all channels of the GER spectrometer are fully co-registered assuring accurate measurement of spectra within each individual pixel without additional spatial corrections. The spectrometer employs a flexible grating based spectrometer unit for the 0.3 - .1.0µ region, and a cryogenically cooled MCT detector for the TIR (8.0 - 12.0µ) band. The cryogenic detector is cooled using a closed cycle sterling cooler. The UV/VIS spectrometer unit provides typically 1 to 10 channels of spectral data. Customized band configurations are available for this system. The spectrometer unit contains all optical components, detector/cooler assemblies and preamplifiers required for parallel measurement of all defined spectral channels.
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The spectrometer is coupled to the Kennedy scanner via a selectable aperture that determines the instantaneous field of view of the system. A precision spectral splitter splits the light passing through the aperture into a thermal component that is reflected, then collimated and focused onto a thermal detector. The transmitted light contains wavelengths below 1.2µ. This light is collimated and dispersed by a precision defecation grating which separates the collimated beam into is spectral components. These components are focused onto the Si detector array with elements aligned to the desired wavelength positions. Alternate visible band positions are available upon request.
Recorded Channels Band Definition
(Microns)1 0.300 - 0.400 2 0.600 - 0.700 3 8.00 - 12.00
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The electrical connection to the spectrometer head is made through a high-density signal connector with an airborne compatible locking connector and a power distribution cable of similar design. The spectrometer module is a sealed unit that can be conveniently opened for maintenance if required. The spectrometer module can be removed from the scanhead module and reinstalled if required without loss of optical alignment.
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The spectrometer uses two detector assemblies. The UV/VIS channels are implemented using a single integrated Silicon detector array. The Thermal channel uses a MCT element integrated into a closed cycle sterling cooler Dewar assembly.
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The electronics module provides all required control functions for operation of the scanner, real-time display, data acquisition and recorder functions. Included is a color monitor suitable for in-flight image analysis. The electronics module contains an intelligent controller incorporating powerful sun compatible workstation boards. This approach provides configuration flexibility, control of system functions, extended on-board diagnostics, and several optional data display functions.
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The electronics consist of the following functional modules: the control module, the data acquisition module, the motor control module, the Sun compatible workstation module, memory board, blackbody heater control and the system display. This is shown in the figure of the Block Diagram below. The control module is contained on a single board and coordinates the data acquisition and data recording. Control signals from the encoder provide scan mirror position and speed information to the control module. The module uses this data and data from the roll gyro to determine pixel position and timing for both the image and reference areas to be measured. This control module then provides all timing and control signals required by the data acquisition, workstation and motor control modules. All major parameters are software selectable and are accessed through the operating/real-time display software. The data acquisition module contains patented GER dedicated, integrated, and hold circuitry, 16 bit A/D conversion hardware, and dual memory buffers for each channel of spectrometer data. In addition, required bus interface and data formatting functions are included for the coordination and transfer of multiple channels of data on each data acquisition card. The data acquisition card receives timing information from the control module and a preamplified signal from each spectrometer channel. The signals from the control module coordinate the sampling, integration, conversion and data manipulation/transfer processes of the data acquisition channels. These processes are synchronized to the scanning mirror. Dual buffer memories are provided to allow simultaneous data transfer and conversion operations to take place providing maximum system capability. The motor controls are intelligent controllers that are accessible through the control software and provide real-time control of motor. The workstation module accesses the data acquisition module data via the standard VME bus and coordinates the flow of data to the recorder module using high speed SCSI. The workstation also integrates GPS; navigational and other desired data into the recorded data. In addition to the data path function, the workstation also provides simultaneous display of selected scanner channels in a real-time waterfall or snapshot display format. (For other features, see the description of HyperView™)
EPS Scanner System
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The electronics module is packaged in standard rack mountable boxes. The system uses an industry standard VME rack and bus system. Required power supplies are integrated into the VME rack system. The functional components of the electronics module are contained in easily replaceable boards and modules that can be serviced in the field. Many field installable expansion options are also available .
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The recording module consists of an Exabyte Mammoth or other compatible Small Computer System Interface (SCSI) tape recorder and all necessary electronics, software drivers, and interfaces.
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The Exabyte is a high speed/high capacity data recorder. Exabyte Mammoth recorders will support up to 100 scans per second operation with the EPS M system.
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Since the recording is done through the industry standard high speed SCSI, any such recording device can be connected to the system without modification of either the GER hardware.
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The scanner interface to the aircraft includes two parts: (1) a Mechanical Interface, and (2) an Electrical Interface.
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The scanner and spectrometer modules are provided with a shock and vibration isolated mounting frame. This frame will be adapted to meet the installation requirements. The mount is usually bolted to the aircraft frame. The electronics are built in standard mount 19" rack mountable boxes.
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The power required for the system is derived from the aircraft system. Typically 28V is available from the aircraft. GER provides a power distribution box within the control electronics package that connects to the aircraft's 28V-power source. This box supplies all system power required. The GER power distribution box includes an AC inverter for operation of the Exabyte recorder and other A. C. powered components as required.
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Real-Time Display & Control Systems
GER HyperView™
software allows the operator to control the scanner and view the data either in real-time during acquisition or after the data are recorded. The software runs on a SPARC workstation and has a graphical, point-and click interface, facilitating use in difficult operating conditions. The software can be used to control the scanner, see data in real-time during collection, or review data collected earlier. The software records and displays the image data in two modes. The first is full spectrum mode, where continuous strips of imagery are collected with all spectral bands. The second mode is termed "snapshot," and is for quick download of selected bands in selected geographic areas. The snapshot mode is meant for time-critical situations such as emergency response and law enforcement. The sections below describe in more detail the user interface and the instrument control system for the basic HyperView™ configuration for operation of the EPS M Series.
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Airborne User InterfaceThe user interface to the EPS M Series is primarily contained in software and consists of an integrated keyboard, computer screen, and trackball. Large on-screen buttons and menus are used to control the system. A touch screen operation is available.
The Waterfall Display Window provides the operator with a dynamic, continuously updated view of the sensor data stream. Menu controls are provided to permit selection and placement of bands and to configure snapshot and display options. In the Waterfall Display Window, the operator can display multiple bands as either multiple grayscale displays or as a single color composite display. A label at the top of the display window identifies each band. The operator can select grayscale, false color, and thresholding or inverted display modes. Various corrections (such as aircraft roll) can be selected in the real-time waterfall display.
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The operator can select a static display window, where either a single band or a color composite of multiple bands can be viewed at full resolution. There is the capability to select a histogram display, contrast enhancement, or color lookup table operations in the static image display, as well as scroll and pan, and the ability to save the screen image as a file.
Airborne Control SystemThe HyperView™
software can be used in two distinct modes of operation - survey and reconnaissance. In the survey mode, full spectral data are collected over a large geographical area. The data are recorded for later analysis and processing on the ground. In this mode, the role of the software is to assist the operator in the operation of the scanner and real-time monitoring of the acquired data. In the reconnaissance mode, the emphasis is on near real-time display of data for quick analysis and decisive action typically required during an emergency response. The data may be recorded on tape as full spectral data or recorded on tape or disk as snapshots. In this mode, the recording of snapshots may be continuous, or controlled by the operator. is the primary interface between the operator and the scanner. In addition to displaying images and controlling the scanner, HyperView™ allows the operator to select the following:
Operating modes of the scanner Scanner operating parameters Recording medium Embedding of GPS data into data files Source of data for image display Operation of tape drive Recording mode
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APPENDIX - EPS-M SERIES SPECIFICATIONS
Technical Specifications (Typical)
Wavelength Range:
3.0µ to 12.0µ0.3µ - 0.4µ : 1 channel
0.6µ - 0.7µ : 1 channel
8.0µ - 12.0µ : 1 channelOptical Collecting Aperture 24cm2 (sensor aperture) IFOV 6.0 mRad System Swath Angle 90° appoximate System Scan Speed Up to 100 Hz Pixels per line Approximately 512 (nominal)
(up to 1024 - software controlled)Recording Media Exabyte or other SCSI compatible device System Controller SUN workstation with high resolution color monitor
General I/O ports are available for other navigation information and peripherals
(Disks, printers, plotters, etc.)Detectors Si array : UV/VIS/NIR
MCT : Thermal, closed cycle coolingMTFB 600 hrs. Power 28 V, 40 AMP standard aircraft power SNR Based on 50% albedo, 45° sun angle, 6.0 mRad IFOV VIS/NIR 100:1 NEDT
(8 - 12 micron)better than 0.2°K Blackbodies
(optional)Two on board for in-flight thermal calibration Geometric Correction Roll axis gyroscope accurate to less than one pixel
Optional Yaw/Pitch gyro dataAbsolute Positioning General data port accepts GPS data
Data are recorded on each scan line
Frequency is dictated by GPS update rateRadiometric Resolution 16 bits
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Mechanical Specifications (approximate)
SCANNER: Length 45cm. 18in. Width 41cm. 16in. Height 50cm. 20in. Weight 16kg. 35lbs.
RECORDING MODULE: Length 67cm. 26in. Width 60cm. 24in. Height 102cm. 40in. Weight (including rack) 80kg. 175lbs.
Under Operation:
Temperature Relative Humidity Raiometric and Scanning Unit -20° to 60°C 0 to 95%
(non-condensing)Control and Monitoring System -10° to 60°C 0 to 95%
(non-condensing)
Out of Operation:
Temperature Relative Humidity Raiometric and Scanning Unit -40° to 60°C 0 to 95%
(non-condensing)Control and Monitoring System -40° to 60°C 0 to 95%
(non-condensing)
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