5.10 SPOT

5.10 SPOT

SPOT was first launched in February, 1986 by the French Government. SPOT-2 was launched in February, 1990 and is now in operation. SPOT-3 will be launched in 1993. SPOT has two HRV (High Resolution Visible imaging system) sensors with stereoscopic and oblique pointing functions. Figure 5.10.1 shows the general configuration of SPOT.

a. Orbit
Altitude; 830 Km, Inclination; 98.7,
Sun synchronous and semi-recurrent orbit,
Time of passage of the equator; 10:30a.m.,
Recurrent : 26 days nominally but 4 - 5 days
if observed with oblique pointing.

b. Sensors
HRV is not an optical-mechanical sensor but a linear CCD (charge coupled device ) camera with an electronic scanning system. Table 5.10.1 shows the HRV characteristics for the three multi-spectral bands with 20 m IFOV, and a panchromatic mode with 10 m IFOV.

HRV can change the look angle by changing the pointing mirror angle by up to +-27 degrees, as shown in Figure 5.10.2. The enables it to look at the same position from two different orbits as shown in Figure 5.10.3. Such a sidelooking function produces stereoscopic images, with a baseline to height ratio (B/H ratio) of up to 1, for measurement of topographic elevation.

c. Data
A scene of HRV has a nadir coverage of 60 x 60 km, but an oblique coverage of 81 km square, at maximum look angle of 27. Each scene is coded with column number (K) and row number (J), termed the GRS (SPOT Grid Reference System).

Each node is basically given for a nadir observation with odd numbers of K for the coverage of the first HRV sensor. For the oblique scene, the nearest node to the center of the scene is assigned to that scene.

d. Data Utilization
SPOT data are received at 14 ground receiving stations. The main purpose of data utilization is for land area observation as well as for topographic mapping at scales 1/50,000 and smaller.

Sometimes SPOT HRV Panchromatic band (10 m IFOV) and Landsat TM (30 m IFOV) are combined into a color composite for better image interpretation. SPOT panchromatic and multispectral modes are also often overlaid to aid in interpretation.