5.9 Landsat

5.9 Landsat

Landsat-1 was launched by the USA in 1972, and was the first earth observation satellite in the world, which initiated the remarkable advance of remote sensing. To date, five Landsat's (Landsat 1-5) have been launched, with only Landsat 5 still in operation.

Figure 5.9.1 shows the general configuration of Landsat 4 and 5.

a. Orbit of Landsat 4,5 and 6
Altitude; 705 km, Inclination; 98,
Sun synchronous and semi-recurrent orbit,
Time of passage of the equator; 9:39a.m.,
Recurrent: 17 days
Swath: 185 km

b. Sensors
(1) MSS (multispectral scanner)
(2) TM (thematic mapper)

Both the sensors are optical-mechanical scanners.

Table 5.9.1 shows the bands, wavelength and resolution of MSS and TM. Landsat 6 will have only ETM (enhanced thematic mapper) with an additional panchromatic mode with 15 meter resolution.

c. Data
MSS and TM data are composed in a unit of scene with a size of 185 x 170 km. Each scene is coded with path number and row number, based on what is called WRS (world reference system). For example, Japan is covered with about 63 scenes of path number 104 - 114 and row numbers 28 - 42. Image data are recorded with respect to each pixel with a numerical value (V) of 8 bits (0 - 255). The absolute radiance R (mW / cm.sr ) can be computed by the following formula.

R = V[ ( Rmax - Rmin ) / Dmax ] + Rmin

where Rmax : maximum recorded radiance
Rmin : minimum recorded radiance
Dmax: 255 for TM
127 for MSS

Table 5.9.2 and Table 5.9.3 show Rmin and Rmax of TM and MSS respectively. One should note that the radiances Rmax and Rmin are measured onboard but not on the ground. Therefore they include atmospheric influences.

d. Data Utilization
There are 15 Landsat receiving stations in the world from which Landsat data are distributed to users for resources management and environmental monitoring.