Unit conversion coefficients, which are defined as radiance per 1DN, are used to convert from DN to radiance.
Radiance (spectral radiance) is expressed in unit of W/(m2•sr•μm).
We undertake to maintain the unit conversion coefficient at the same values throughout the mission's life.
The relationship between DN values and radiances is shown below and illustrated in Figure 5-5.
A DN value of zero is allocated to dummy pixels.
A DN value of 1 is allocated to zero radiance.
A DN value of 254 is allocated to the maximum radiance in the VNIR and SWIR bands.
A DN value of 4094 is allocated to the maximum radiance in the TIR bands.
A DN value of 255 is allocated to saturated pixels in the VNIR and SWIR bands.
A DN value of 4095 is allocated to saturated pixels in the TIR bands.
Figure 5-5 Relationship between DN values and radiances
The maximum radiances depends on both the spectral bands and the gain settings and are shown in Table 5-3.
Table 5-3 Maximum radiance
Band No.
Maximum radiance (W/(m2•sr•μm))
High gain
Normal gain
Low gain 1
Low gain 2
1
170.8
427
569
N/A
2
179.0
358
477
3N
**106.8
218
290
3B
**106.8
218
290
4
27.5
55.0
73.3
73.3
5
8.8
17.6
23.4
103.5
6
7.9
15.8
21.0
98.7
7
7.55
15.1
20.1
83.8
8
5.27
10.55
14.06
62.0
9
4.02
8.04
10.72
67.0
10
N/A
28.17*
N/A
N/A
11
27.75*
12
26.97*
13
23.30*
14
21.38*
Note: *Blackbody radiance at 370 K y ** Apparent gain is 2.0412, slightly different from the nominal high gain value of 2.0.
Maximum radiances for high and low gains are basically defined as those for normal gain divided by nominal gain except
for band 3N and 3B at high gain. For band 3N and 3B, the maximum radiance is slightly smaller than the value calculated above,
which may be saturated because of a large offset.
The unit conversion coefficients can be calculated as follows.
