6.3 RADARSAT and Stereoscopy

RADARSAT-1 for stereo imaging

The stereo parallax necessary for a stereo image pair or an anaglyph is created when an object is viewed from two different positions. As with aerial photos, RADARSAT and other satellite image pairs are sequenced from left to right depending on the position of the platform at the time the image was taken. The sequence of a RADARSAT image pair depends on two factors:

• beam position of the sensor, and
• whether the satellite was on an ascending or descending orbital pass.

As noted previously, RADARSAT has the ability to collect data from a range of beam positions. The beam position sets the viewing angles. These are steepest at the first, and shallowest at the last position. On an ascending pass the look direction of the sensor is to the east. The beam positions fan out sequentially towards the east. On a descending pass the sensor faces west and the beam positions fan out towards the west.

Two examples of same-side stereo acquisition using S1 and S3 beam modes of RADARSAT-1

For example, in order to image the same geographical area with an S1 and S3 beam mode and position, both on a descending pass, the S3 satellite orbit will be east or to the right of the S1 satellite orbit. This is due to the fact that S3 has a shallower viewing angle than S1. Thus, the S1 image will take the left hand position of an S1/S3 image pair collected on a descending pass. If both images are collected on an ascending pass, the order of the image pair is reversed.

Example of same-side stereo viewing using S1 and S3 beam modes of RADARSAT-1

Opposite-side stereo acquisition for RADARSAT-1

Opposite-side stereo viewing

In the case of an opposite-side stereo configuration the descending image is viewed on the left hand side while the ascending image is viewed on the right hand side. Such an example is given with descending/ascending ERS-1 images in chapter 7. This sequence may seem reversed to viewers accustomed to viewing optical imagery. However, if we recall that on SAR images, relief displacement is towards the sensor, while on optical images relief displacement is away from the optical sensor, the order makes sense. Remember that a SAR viewing angle, has approximately the same effect as an equivalent oblique optical viewing angle of 90°- .

Angle of view