Bjorn T. Eng

Airborne visible/infrared imaging spectrometer (AVIRIS): recent improvements to the sensor and data facility

AVIRIS operations at the Jet Propulsion Laboratory consist primarily of a sensor task and a data facility task. These two activities are supported by an experiment coordination, a calibration and a management effort. The sensor task is responsible for AVIRIS sensor maintenance, laboratory calibration, and field operations. The AVIRIS data facility is responsible for data archiving, data calibration, quality monitoring and distribution. In this paper we describe recent improvements in these two primary AVIRIS tasks. The inflight performance of AVIRIS in 1992 and 1993 that resulted from these improvements is also presented.

Thermal infrared spectral imager for airborne science applications

An airborne thermal hyperspectral imager is underdevelopment which utilizes the compact Dyson optical configuration and quantum well infrared photo detector (QWIP) focal plane array. The Dyson configuration uses a single monolithic prism-like grating design which allows for a high throughput instrument (F/1.6) with minimal ghosting, stray-light and large swath width. The configuration has the potential to be the optimal imaging spectroscopy solution unmanned aerial vehicles (UAV) due to its small form factor and relatively low power requirements. The planned instrument specifications are discussed as well as design trade-offs. Calibration testing results (noise equivalent temperature difference, spectral linearity and spectral bandwidth) and laboratory emissivity plots from samples are shown using an operational testbed unit which has similar specifications as the final airborne system. Field testing of the testbed unit was performed to acquire plots of emissivity for various known standard minerals (quartz). A comparison is made using data from the ASTER spectral library.

Towards HyTES: an airborne thermal imaging spectroscopy instrument

An airborne thermal hyperspectral imager is underdevelopment which utilizes the compact Dyson optical configuration and quantum well infrared photo detector (QWIP) focal plane array. The Dyson configuration uses a single monolithic prism-like grating design which allows for a high throughput instrument (F/1.6) with minimal ghosting, stray-light and large swath width. The configuration has the potential to be the optimal imaging spectroscopy solution unmanned aerial vehicles (UAV) due to its small form factor and relatively low power requirements. The planned instrument specifications are discussed as well as design trade-offs. Calibration testing results (noise equivalent temperature difference, spectral linearity and spectral bandwidth) and laboratory emissivity plots from samples are shown using an operational testbed unit which has similar specifications as the final airborne system. Field testing of the testbed unit was performed to acquire plots of emissivity for various known standard minerals (quartz). A comparison is made using data from the ASTER spectral library.

Implementation of a very large atmospheric correction lookup table for ASTER using a relational database management system

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is designed to provide a high resolution map of the Earth in both visible, near-infrared, and thermal spectral regions of the electromagnetic spectrum. The ASTER science team has developed several standard data product algorithms, but the most complex and computing-intensive of these is the estimation of surface radiance and reflectance values, which is done by modeling and correcting for the effects of the atmosphere. The algorithm for atmospheric correction in the visible bands sensed by ASTER calls fur the use of a very large atmospheric correction look up table (ACLUT). The ACLUT contains coefficients which describe atmospheric effects on ASTER data under various conditions. The parameters used to characterize the atmosphere and its effects on radiation in the ASTER bands include aerosol and molecular optical depth, aerosol size distribution, single scattering albedo, and solar, nadir view, and azimuth angles. The ACLUT coefficients are produced by thousands of runs of a radiative transfer code (RTC) program produced by Phil Slater and Kurt Thome of U. of A. The final version of ACLUT is expected to be in the neighborhood of 10 gigabytes. The RDBMS Sybase is used to manage the process of generating the ACLUT as well as to host the table and service queries on it. Queries on the table are made using ASTER band number and seven floating-point values as keys. The floating-point keys do not necessarily exactly match key values in the database, so the query involves a hierarchical closest-fit search. All aspects of table implementation are described.

Infrared instrument support for HyspIRI-TIR

The Jet Propulsion Laboratory is currently developing an end-to-end instrument which will provide a proof of concept prototype vehicle for a high data rate, multi-channel, thermal instrument in support of the Hyperspectral Infrared Imager (HyspIRI)–Thermal Infrared (TIR) space mission. HyspIRI mission was recommended by the National Research Council Decadal Survey (DS). The HyspIRI mission includes a visible shortwave infrared (SWIR) pushboom spectrometer and a multispectral whiskbroom thermal infrared (TIR) imager. The prototype testbed instrument addressed in this effort will only support the TIR. Data from the HyspIRI mission will be used to address key science questions related to the Solid Earth and Carbon Cycle and Ecosystems focus areas of the NASA Science Mission Directorate. Current designs for the HyspIRI-TIR space borne imager utilize eight spectral bands delineated with filters. The system will have 60m ground resolution, 200mK NEDT, 0.5C absolute temperature resolution with a 5-day repeat from LEO orbit. The prototype instrument will use mercury cadmium telluride (MCT) technology at the focal plane array in time delay integration mode. A custom read out integrated circuit (ROIC) will provide the high speed readout hence high data rates needed for the 5 day repeat. The current HyspIRI requirements dictate a ground knowledge measurement of 30m, so the prototype instrument will tackle this problem with a newly developed interferometeric metrology system. This will provide an absolute measurement of the scanning mirror to an order of magnitude better than conventional optical encoders. This will minimize the reliance on ground control points hence minimizing post-processing (e.g. geo-rectification computations).

QWEST: Quantum Well Infrared Earth Science Testbed

Preliminary results are presented for an ultra compact long-wave infrared slit spectrometer based on the Dyson concentric design. The spectrometer has been integrated in a dewar environment with a quantum well infrared photodetecor (QWIP), concave electron beam fabricated diffraction grating and ultra precision slit. The entire system is cooled to cryogenic temperatures to maximize signal to noise ratio performance, hence eliminating thermal signal from transmissive elements and internal stray light. All of this is done while maintaining QWIP thermal control. A general description is given of the spectrometer, alignment technique and predicated performance. The spectrometer has been designed for optimal performance with respect to smile and keystone distortion. A spectral calibration is performed with NIST traceable targets. A 2-point non-uniformity correction is performed with a precision blackbody source to provide radiometric accuracy. Preliminary laboratory results show excellent agreement with modeled noise equivalent delta temperature and detector linearity over a broad temperature range.

Characterization and performance of the Prototype HyspIRI-TIR (PHyTIR) Sensor

The Prototype Hyspiri-TIR (PHyTIR) instrument was developed under NASA’s instrument incubator program and is now operational in the laboratory. The scan head uses state-of-the-art focal plane technology to rapidly acquire data from an eight inch telescope focused at infinite, reflective relay and continuously rotating scan mirror. A series of narrowband interference filters are placed in close proximity to the focal plane. Arrays of 256×16 Mercury Cadmium detectors are under each filter. The detectors have their long wave cutoff at 13.2μm. The filters serve to block out unwanted radiation from other spectral channels, hence forming a high performance multi-band imager with the use of the scanning mirror.

High Speed, Multi-Channel, Thermal Instrument Development in Support of HyspIRI-TIR

The Jet Propulsion Laboratory is currently developing an end-to-end instrument which will provide a proof of concept prototype vehicle for a high data rate, multi-channel, thermal instrument in support of the Hyperspectral Infrared Imager (HyspIRI)-Thermal Infrared (TIR) space mission. HyspIRI mission was recommended by the National Research Council Decadal Survey (DS). The HyspIRI mission includes a visible shortwave infrared (SWIR) pushboom spectrometer and a multispectral whiskbroom thermal infrared (TIR) imager. The prototype testbed instrument addressed in this effort will only support the TIR. Data from the HyspIRI mission will be used to address key science questions related to the Solid Earth and Carbon Cycle and Ecosystems focus areas of the NASA Science Mission Directorate. Current designs for the HyspIRI-TIR space borne imager utilize eight spectral bands delineated with filters. The system will have 60m ground resolution, 200mK NEDT, 0.5C absolute temperature resolution with a 5-day repeat from LEO orbit. The prototype instrument will use mercury cadmium telluride (MCT) technology at the focal plane array in time delay integration mode. A custom read out integrated circuit (ROIC) will provide the high speed readout hence high data rates needed for the 5 day repeat. The current HyspIRI requirements dictate a ground knowledge measurement of 30m, so the prototype instrument will tackle this problem with a newly developed interferometeric metrology system. This will provide an absolute measurement of the scanning mirror to an order of magnitude better than conventional optical encoders. This will minimize the reliance on ground control points hence minimizing postprocessing (e.g. geo-rectification computations).

Implementation of the ASTER science standard data product requirements in the EOSDIS system

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is designed to provide a high-resolution map of the Earth in both visible, near-infrared, and thermal spectral regions of the electromagnetic spectrum. The ASTER science team has developed standard data product algorithms to permit the estimation of surface radiances and reflectance values, to calculate surface temperatures both over water and land, to provide a color enhanced product with a high degree of surface discriminability, in addition to other functions. The ASTER product generation system (PGS) team is implementing these requirements within the constraints of the EOSDIS system, using a rapid development methodology that emphasizes open lines of communication in a team approach using concurrent engineering techniques. The PGS development environment was structured both to conform to the changing needs of the EOSDIS system and to incorporate experimentation with and modification of the science algorithms as the software was being developed and tested. This challenging environment required a focus on novel methods of requirements tracking, software interface uniformity, toolkit transparency, and platform independence. This approach required a high degree of interoperability of the software development environment, a well as a flexible and highly integrated configuration management and testing approach. In addition in order to validate the PGS software in the operational environment of the EOSDIS, a remote integration testing approach was adopted to provide a rapid convergence of the final integrated system. This paper describes the critical elements in the development and integration of the ASTER PGS system.