Look Angles and Coverage Area
The EO-1 satellite follows the World Reference System-2 (WRS-2) path and row system with a 16-day nadir repeat cycle.
The sensors on board EO-1 are capable of cross-track pointing to allow potential imaging within one adjacent WRS path in each direction from nadir. This means EO-1 can collect an image on the nadir path, east path with the sensors pointed west, or west path with the sensors pointed east, giving EO-1 three imaging opportunities per 16 days. The west and east path follow seven and nine days after the overhead path, respectively.
While a cross-track pointing sensor can provide flexibility for image acquisitions, an increased look angle may have adverse impacts on the geometric characteristics of a particular scene (i.e. pixel distortion and band-to-band alignment).
The following graphic displays the potential imaging range of a typical pointed sensor. The angles displayed in the image are not exact, but the numbers reported are the actual range of the angles at 30 degrees north latitude.
The look angle associated with a customer's Data Acquisition Request (DAR) will vary depending upon the location of the image target from within the WRS-2 row (Target Range) as well as the latitude of the target. The table below shows the range of look angles for specific latitudes.
Even DARs requested as "within nadir scene only" will have a small look angle. This is because the ALI's standard scene width is 37 kilometers and Hyperion's is 7.7 kilometers, but EO-1 is capable of pointing anywhere within the WRS-2 row. The image below shows the relative footprint of a Hyperion (white) and ALI (yellow) 42 km and 185 km DAR, with respect to a Landsat WRS-2 row (blue). The 185 km footprint is also considered as "within nadir scene only".
The Hyperion footprint is displayed slightly smaller in the graphic to show that there is a misalignment along the western edge in relation to the ALI footprint. The Hyperion footprint is shifted approximately 1.7 km west, with respect to the ALI footprint.
DARs that request either the ALI and Hyperion instruments, or only the Hyperion instrument will have the site lat/lon (red dot) centered based on the Hyperion instrument to guarantee Hyperion coverage.
DARs that request only the ALI instrument will have the site lat/lon centered based on the ALI instrument. Please note that in an ALI centered DAR, the Hyperion instrument will miss the target lat/lon.