the landsat 7 processing system ( lps ) level zero-r science products

1ESDIS HDF-EOS Workshop IVLandover, Maryland, September 20, 2000

The Landsat 7 Processing System( LPS )

Level Zero-R Science Products

Michael R. ReidComputer Sciences Corporation

[email protected]


The Landsat 7 Mission

• The latest in the Landsat series

• Joint operation between NASA and USGS

• Global coverage in 8 bands

• Sun-synchronous orbit

• Landsat 7 successfully launched in April 1999

• Now fully operational

• Data products provided by the USGS’ EROS Data Center (EDC) in Sioux Falls, SD


Earth Coverage

• Enhanced Thematic Mapper Plus (ETM+) is the only science instrument– Images the Earth in 185 km wide swaths– Images in eight bands

• Image data are fitted onto the Worldwide Reference System (WRS) grid– WRS grid consists of 185 km 170 km scenes– ETM+ images a WRS scene with 375 scans

• WRS scenes overlap


The ETM+ Instrument Data

• Eight bands– Six 30m-resolution spectral bands

• Bands 1-5 (range = 0.45…1.75 m)

• Band 7 ( = 2.09-2.35 m)

• 6,600 pixels per scan data line

• 16 data lines per scan

– One 60m-resolution thermal band• Band 6 ( = 10.4-12.5 m)

• 3,300 pixels per scan data line


– One 15m-resolution panchromatic band• Band 8 ( = 0.52-0.90 m)

• 13,200 pixels per data line



Landsat 7 Processing System (LPS)

• Developed at NASA/GSFC for the EDC

• Part of the Landsat 7 Ground System

• Performs the first stage of Level 0 processing– Aligns bands (forward and reverse scans)– Does not apply corrections or calibrations– Does not perform rectification

• Produces HDF-EOS science data products on a subinterval basis

• Runs on a high-end SGI™ system


LPS Processing

• Divides the subintervals into sets of contiguous WRS scenes

• Geolocates the scenes

• Produces viewable, multi-band, color browse images on a WRS scene basis

• Performs automatic cloud cover assessment (ACCA) on a WRS scene basis

• Displays a Moving Window Display to the user


The LPS Moving Window Display (MWD)


LPS Processing continued…

• Receives data on two channels (“format 1” and “format 2”)

• Decodes the downlinked raw telemetry

• Processes the two formats separately

• Constructs an image in each band of the “swath” on the Earth’s surface covered during a contact

• Divides the swath into subintervals


The LPS Data Products

• LPS products generated on a subinterval basis

• Format 1 and Format 2 are separate file sets

• The LPS Product file sets include:– Band files (Swath files)– Internal Calibrator (IC) data files– Mirror Scan Correction Data (MSCD) files– Payload Correction Data (PCD) files– Metadata files– Multi-Band Browse files (format 1 only)


The Band Files — Swaths

• Image data stored in HDF-EOS Swaths– One Swath per file

• Bands 1-5 & 7 files are up to about 1.2 Gb in size

• Band 6 files are up to about 295 Mb in size

• Band 8 data are huge, won’t fit in single files– Up to about 4.6 Gb of data in a 35-scene

subinterval– HDF 4 limits file sizes to 2 Gb– Written to up to three separate swaths in separate

segment files


The Band Files — Geolocation

• Geolocation structures– Uses HDF-EOS Index map to link WRS scene

corner lon/lat coordinates to the Swath• Full scenes from 30m-res. bands are always 6,000 data

lines

• Partial scenes at the beginnings and ends of subintervals are of irregular sizes

– Uses Time Geolocation field to temporally locate scans in the Swaths

• HDF-EOS Geolocation structures also used to store other ancillary data


The Internal Calibrator (IC) Files

• Contain lamp and shutter data for spectral bands

• Contain blackbody radiance and shutter data for thermal band (band 6)

• One file for each format– Separate HDF-EOS Swath for each band

• One data set per scan

• Data located by Time only using HDF-EOS Geolocation structure


Mirror Scan Correction Data (MSCD) Files

• Mainly contain data quality information

• Stored in an HDF-EOS Point

• Located by Time only using HDF-EOS Geolocation structure

• Format 1 and Format 2 MCSD are identical except for start and end offsets at the beginnings and ends of the data


Other LPS Product Files

• Payload Correction Data (PCD) Files– Contain spacecraft attitude and ephemeris information and

miscellaneous engineering data

– Native HDF Vdata, no HDF-EOS structures

– Format 1 and Format 2 are identical

• Metadata Files– Format 1 and Format 2 similar, but not identical

– Simple text file in Object Definition Language (ODL) Syntax

• Browse Files– Format 1 only

– One native HDF RIS24 true color image

– Made from three of the five format 1 spectral bands

– JPEG Compressed images


LPS Browse File (Hudson Bay)


Format 1

• Six Band files– Bands 1-5 and 6L

• One Internal Calibrator (IC) data file

• One Payload Correction Data (PCD) file

• One Mirror Scan Correction Data (MSCD) file

• One Metadata file– Includes scene cloud cover assessments

• 1 to 37 Multi-band Browse files


Format 2

• Three Bands, up to five files– Bands 6H and 7– Band 8 (High-Resolution Panchromatic Band)

• Written to up to three segment files due to size

• One Internal Calibrator (IC) data file

• One Payload Correction Data (PCD) file

• One Mirror Scan Correction Data (MSCD) file

• One Metadata file

• No Browse files


The LPS Product File Set


Level Zero-R Data Subsets

• Single WRS scene products– One 375 scan subset

– Data fitted to the WRS grid

• Multiple scene products– Contains several contiguous WRS scenes

• Partial subinterval (a.k.a., floating scene) products– Similar to the multiple scene products, but not aligned along

WRS rows

• Full subinterval products– Essentially the full LPS subinterval


Subsetting the LPS Subintervals

• LPS Band and IC files contain geolocated HDF-EOS Swaths– Can subset band data by index-mapped WRS scene corner

geographic coordinates or time using HDF-EOS functions• Band 8 presents a problem due to file segmentation

– Can subset IC data by time using HDF-EOS functions

• MSCD file contains an HDF-EOS Point– Can subset by time using HDF-EOS functions

• PCD is native HDF and cannot be subsetted using HDF-EOS functions


LPS Subsetting Difficulties

• Band data Swaths are stored in separate files

• Format 1/Format 2 data offset

• Partial subinterval geolocation– LPS only computes lon/lat coordinates for WRS

scene corners, not on a scan basis– Must interpolate subset interval corner coordinates

• Band 8 segmentation– HDF-EOS does not support file segmentation


Band 8 Subsetting Problem

• Must treat the band 8 segments as completely separate data sets

• Subsetting out multiple scene or partial subinterval products from band 8 is especially complicated if the subset interval spans across segments

• After subsetting from the two segments, the data must be concatenated into a single array


Level Zero-R Distribution Product

• Native HDF, no HDF-EOS structures• Contains data from both Format 1 and Format 2• Subsets of Band and IC data written to Scientific

Data Sets (SDS)• Subset of MSCD written to Vdatas• Complete PCD and Metadatas written to Vdatas• Contains Calibration Parameter File (CPF)• Stores all data in HDF external elements


L0R Distribution Product File Set

the landsat 7 processing system ( lps ) level zero-r science products

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