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ASTER Processing

ASTER Front-End Processing Flow

• Level-0 data is received by EDOS through TDRSS/White Sands Complex, NM
• EDOS sends Level-0 data to the Japanese Ground Data System (GDS)
• GDS processes Level-0 to Level-0A in the Front-End Processing Module which includes:
  • Depacketizing Level-0 Data: The packets for each group (VNIR, SWIR, & TIR) are depacketized and aligned to recover the instrument source data. The spectral band information is multiplexed with the image in BIP format.
  • Demultiplexing Instrument Source Data: The instrument source data are demultiplexed to separate image data for every spectral band in BSQ format.
• SWIR & TIR Image Data Stagger Realignment: SWIR & TIR image data are re-aligned to compensate for a staggered configuration. Their Level-0 pixel addresses are changed such that all the pixels for each band lie on one line.

ASTER Data Processing from Level - 0 to Levels 1A and 1B

• Following the front-end processing, radiometric and geometric system corrections are calculated and the coefficients appended to form Level-0B data.
• Scene-cutting is carried out on Level-0B data according to the World Reference System (WRS), and a set of geolocation data is generated for each scene to produce Level-1A data.
• Level-1A data product contains the image data, and appended radiometric coefficients, geolocation data, and auxiliary data.
• Level-1B data product is generated by applying these radiometric calibration and geometric resampling data. Level-1B is the input data for all the derivative geophysical data products.

Radiometric and Geometric Calibration

Radiometric Calibration

Pre-Flight Calibration: In the pre-flight phase, observation unit or scene-specific radiometric coefficients are generated at pre-defined reference temperatures. The performance behavior of gain, offset, sensitivity, signal-to-noise ratio, MTF, stray light, & bright target recovery are measured & converted to radiometric calibration coefficients (RCC) and temperature coefficients. These form the contents of the RCC database. These RCCs were evaluated using integration spheres, whose radiance is traceable to a known blackbody.

Post-Launch Calibration: This will be achieved using on-board calibrators and by vicarious methods. An on-board system enables end-to-end sensor calibration using the full aperture of the sensor, covering its entire field of view, and the full spectral range of the instrument. Vicarious calibration helps determine the absolute calibration coefficients for a small number of detectors in each sensor. This aids in adjusting the relative calibration for all the detectors.

During the Level-1 product generation phase, corrections are applied to the radiometric coefficients for instrument conditions such as detector & dewar temperatures. During the Initial Checkout period, destriping parameters will be generated upon analysis of the image data, if necessary.

Geometric Calibration

Pre-Flight Calibration: This is an off-line process to generate geometric parameters such as Line of sight Vectors (LOV) of the detectors and pointing axes information evaluated toward the Navigation Base Reference (NBR) of the spacecraft deemed to reflect on the instrument accuracy & stability. These are stored in the geometric correction database.

Post-Lauch Calibration: After launch, these parameters are to be corrected through validation using Ground Control Points (GCPs) and inter-band image matching techniques.

Geometric system correction entails the following processes:

• Pointing correction
• Coordinate transformation from spacecraft coordinates to the orbit coordinates
• Coordinate transformation from orbit coordinates to the earth's inertial coordinates
• Coordinate transformation from earth's inertial coordinates to Greenwich coordinates

Improving Band-to-Band registration accuracy through image-matching involves 2 processes:

• SWIR parallax correction
• Inter-telescope registration process

ASTER Routine versus On-Demand Processing

ASTER is unique among all the Terra instruments & data products derived therefrom in that it allows a distinction to be made between routine & on-demand data acquisition and product generation.

Routinely acquired data and data products generated include: Level-1A and Level-1B for all 3 subsystems (VNIR, SWIR, & TIR).

On-demand products include: Decorrelation Stretch , Brightness Temperature, Surface Reflectance, Surface Radiance, Surface Emissivity, Surface Kinetic Temperature, Polar Cloud Classification and Digital Elevation Model (DEM). On-demand data acquisition is accomplished through the Data Acquisition Request (DAR) process.

Data Acquisition Request (DAR) Concept

A Data Acquisition Request (DAR) is a request to schedule and acquire data with specific spatial and temporal parameters. Any authorized user can submit a request to acquire data via the ASTER DAR Tool. The ASTER Science Team has a number of outstanding data acquisition requests that cover different parts of the world. Large data acquisitions on behalf of the science community are made through Science Team Acquisition Requests or STARS. There are 3 types of STARS: STARS-local, STARS-regional, & STARS-global. If the desired ASTER observations have not yet been acquired or even requested, anyone can apply to become authorized to submit DARs via the DAR Tool.�For more information on obtaining DAR privileges please visit http://asterweb.jpl.nasa.gov/gettingdata/

Note: anyone can use the ASTER DAR Tool as a guest to search for existing DARs and their status'.

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