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Airborne: Texas Develops Hyperspectral Airborne Imaging Spectrometer
By Alfredo E. Prelat Introduction
Remote sensing is usually defined as the process of obtaining information about an object without actual physical contact. Vision and photography are two examples of remote sensing with which everyone is familiar. Both rely on the detection of reflected light in a very narrow wavelength range, referred to as the "visible" range.
All objects absorb and reflect incident radiation to varying degrees depending upon their composition and the wavelength of the energy. As a result, each type of ground cover has a characteristic reflectance curve, sometimes called a "spectral signature." Because the remote sensors now in use can detect energy in a broad wavelength range, analysts can identify and quantify ground cover by comparing these spectral signatures.
Although the currently available sensors have provided valuable data for exploration and environmental studies, they are not without drawbacks. First and foremost among the deficiencies is that optical sensors are hampered by clouds. Radar waves, on the other hand, can penetrate cloud coverage. Secondly, the systems now in operation are limited by their spectral and spatial resolution, i.e., the number of bands they record and their ground resolving power. Thirdly, it can require days or even weeks to obtain data.
Texaco has contracted to develop a hyperspectral airborne imaging spectrometer that will circumvent the problems associated with current sensors. The new system is called the Texaco Energy and Environmental Multispectral Imaging Spectrometer (TEEMS), shown on page 49. This state-of-the-art scanner will collect data in an unprecedented number of channels throughout the ultraviolet (UV), visible (VIS) and infrared (IR) portions of the electromagnetic spectrum. It also integrates synthetic aperture radar (SAR) for all-conditions data collection. The system control uses an on-board workstation to provide real-time monitoring.
The system will have the unique capability of acquiring information with an optical imaging spectrometer and synthetic aperture radar (SAR) simultaneously from the same platform. Data acquisition with geo-referencing and co-registering of UV, VIS, NIR, SWIR, TIR, and SAR channels will be achieved in one flight path.
The imaging spectrometer system will have state-of-the-art optical scanner and multiple spectrometers to cover UV, VIS, NIR, SWIR and TIR. Spectrometers are designed to meet the application requirements of Texaco. All spectrometer band centers, band widths and S/N are selected by Texaco for specific applications. The spectral data will be fully calibrated. The system control uses a state-of-the-art on-board real-time workstation. Real-time data monitoring and geo-referencing are standard. The imaging spectrometer is mounted on a fully stabilized platform. The recording system is flexible and expandable.
The SAR is built as an independent system connected via communication links to the imaging spectrometer controller workstation. The radar system still has an on-board real-time quick look capability for real-time reconnaissance for oil spill monitoring. For exploration and other applications, the data are recorded and processed later on a ground processing computer. TEEMS Flight Segment
The TEEMS Flight Segment contains two core sections: Data Collection; and, System Control and Data Manipulation Data Collection
The data collection section includes: (1) a Kennedy-type optical scanner, spectrometers, fully stabilized platform and on-board calibration. (2) A Synthetic Aperture Radar (SAR) which includes antenna and radar processor. The two parts are fully integrated through the controller. System Control and Data Manipulation
The system control and data manipulation section contains a VME based real-time computer and SUN workstation. The collected data can be processed in real-time (e.g. calibration, georeferencing and others). The raw data or processed data can be recorded on a data recorder. The output of the processor can go to real-time monitor and/or optional real-time data up/down link. TEEMS Ground Segment
The TEEMS ground segment is an enhanced ground processing station. It imports data from either the data tape or data link. The laboratory calibration information will be read in during data input. System pre-processing will be performed in batch mode in a production environment. Output data will be recorded in output (data tape, optical disk, etc.) for application of general users. Applications
One of the primary applications for the Texaco airborne remote sensing system is hydrocarbon exploration. It is expected that the system will provide detailed surface structural mapping; identification of outcrop lithology and mineralogy; drill-site planning and seismic program location; and, identification of hydrocarbon seeps.
Environmental applications also appear to be an area to benefit from TEEMS. Mapping environmental framework for site and operations planning; early identification of environmentally sensitive areas; and real-time, day/night, all weather oil spill monitoring. Also, the system will have the ability to monitor exploration and production facilities, and it will be effective in bench marking - establishing baseline of physical/biological conditions.
Other applications for TEEMS include mineral and geothermal exploration, agricultural, hydrology, forestry, engineering, GIS, and land cover and land use classification. Conclusion
It is expected that TEEMS will provide Texaco with the highest resolution image spectrometer available to industry; the first imaging spectrometer fully integrated with radar; full on-board stabilization and real-time calibration; and on-board geo-referenced data displayed in real-time. About the Author:
Alfredo E. Prelat is principal scientist with Texaco's E&P Technology Department. He may be reached at 713-954-6023 (phone) or 713-954-6113 (fax).
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