circfp - Compute elliptical footprints resulting from circular iFOVs

Berke Durak bd@exhrd.fr

DESCRIPTION

Computes the parameters of an ellipse resulting from the intersection of a cone and an ellipsoid.

Used for calculating the theoretical footprints of spaceborne sensors having a circular field-of-view.

The satellite position can also be estimated from the observation geometry (observation point and view angles) and the satellite height.

This allows IASI footprints to be calculated from information contained in the L1C NAT files. The IASI instruments are spectrometers onboard the Metop satellites that do whisk-broom scanning with a group of 2x2 circular pixels.

METHOD

The view cone is sampled using a finite number of rays. These produce 3D intersection points on the ellipsoid. Quadratic parameters are extracted using a least-squares fit, and these are converted to 2D ellipse parameters expressed on the tangent geodetic basis at the observation point. For the ray-ellipsoid intersection, a linear transformation ("unsquishing") converts the ellipsoid into a sphere to allow a closed-form intersection formula to be used.

Author and links

Author: Berke DURAK bd@exhrd.fr

• https://exhrd.fr/
• https://github.com/berke
• https://github.com/berke/circfp
• https://crates.io/crates/

Keywords

• Cone, sphere, ellipsoid, intersection, ellipse, observation geometry, circular field of view, footprint, remote sensing, satellite, IASI

Revision history