Remote Sensing DefinitionsΒΆ

  • Field of View (FOV) is the doubled half-angle describing the viewing extent of a camera.

    _images/fov.png

    In the figure, β„“ is sensor length and f is focal length. FOV is approximately the ratio of these values:

    \[FOV = 2\theta_H = 2\tan^{-1}\left(\frac{β„“/2}{f}\right) \approx \frac{β„“}{f}\]

    For cameras with different horizontal and vertical lengths, both HFOV and VFOV are specified.

  • Instantaneous Field of View (IFOV) is the doubled half-angle describing the viewing extent of a single pixel, i.e. the spatial resolution. This value is derived as shown in the FOV section, but with sensor length replaced by pixel length (a.k.a pixel pitch). For a single-pixel detector, FOV = IFOV.

  • Sampling Distance or Ground Sample Distance (GSD) is the distance between pixel centers in the object plane; a measure of spatial resolution for a specific object plane distance and orientation. Sample distance is the general term and GSD is used for downward-looking aircraft and satellites. When the object plane is perpendicular to the optical axis,

    \[GSD_\perp = h*2\tan\left(\frac{IFOV}{2}\right) \approx h*IFOV\]
  • Resolvable Distance or Ground Resolved Distance (GRD) is the spatial extent of the smallest resolvable feature. Resolvable distance is the general term and GRD is used for downward-looking aircraft and satellites. This number is twice the sampling distance (see above) in accordance with the Nyquist sampling theorem.