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11.1 Level 0R Product | Menu |
Unlike earlier Landsat programs, the Landsat 7 system was not originally designed to produce high level (i.e. Level 1) products for users. The baselined program philosophy was to provide raw data only which would leave the value added domain for commercial companies. A prevailing "wait and see" position by commercial vendors prompted NASA to add a systematiccorrection capability to ensure product availability. The primary product for users and vendors seeking higher level processing, however, is 0R data - an essentially raw data form that is marginally useful prior to radiometric and geometric correction. This is readily apparent when viewing a simulated 0R image . A Landsat 7 0R product, however, does contain all the ancillary data required to performthese corrections including a calibration parameter file (CPF) generated by the Landsat 7 IAS.
LPS spatially reformats earth imagery and calibration data into Level 0R data. This involves shifting pixels by integer amounts to account for the alternating forward-reverse scanning pattern of the ETM+ sensor, the odd-even detector arrangement within each band, and the detector offsets inherent to thefocal plane array engineering design. All LPs 0R corrections are reversible; the pixel shift parameters used are documented in the IAS CPF.
The LPs 0R output is HDF-EOS formatted and archived. Details of the archival format can be found in the Landsat 7 System Wideband DFCB, Vol. 4.
11.1.1 Product Size
Three options, depicted in Figure 11.2, exist when defining the size or spatial extent of aLandsat level 0R product ordered from the LP-DAAC.
* Standard Worldwide Reference System (WRS) Scene. The standard WRS scene as defined for Landsats 4 and 5 was preserved as a product for Landsat 7. The WRS indexes orbits (paths) and scene centers (rows) into a global grid system comprising 233 paths by 248 rows. The path/row notation was originally employed to provide a standard designator forevery nominal scene center and allow straight forward referencing without using longitude and latitude coordinates.
The distance between WRS center points along a path is 161.1 kilometers. A path distance of 90 kilometers before and after a WRS center point defines the standard scene length of 180 km. This length includes 20 scans of overlap with neighboring scenes. The standard WRS scene overlapsneighboring scenes along a path by 5% at the equator and has a width or cross track distance of 185 kilometers.
Landsat 7 browse is framed according to WRS scenes. An ordered scene will cover the same geographic extent observed in the browse with the following caveat. Standard WRS scenes have 375 scans. Partial scenes (less than 375 scans) may exist at the beginning or end of a subinterval dueto the fact that imaging events do not always start and end on scene boundaries. Browse and scene metadata for these occurrences accurately reflect their partial scene nature and geographic extent although partials are currently not offered due to complexities associated with level 1 processing.
* Subinterval. An interval is a scheduled ETM+ image period along a WRS path, and may be from one to90 scenes in length. A subinterval is a contiguous segment of raw wideband data received during a Landsat 7 contact period. Subintervals are caused by breaks in the wideband data stream due to communication dropouts and/or the inability of the spacecraft to transmit a complete observation (interval) within a single Landsat 7 contact period. The largest possible subinterval is 35 scenes long. Thesmallest possible subinterval is a single ETM+ scene.
* Partial Subinterval A partial Landsat 7 subinterval can also be ordered. The partial subinterval is dimensioned according to standard WRS scene width, is at least one WRS scene in length, and can be up to 10 scenes in length if ordered in 0R form or 3 scenes in length in 1G form. A partial subinterval can float or be positioned at any...