TIRS requirements are specified in a manner similar to the OLI requirements. The specifications require TIRS to collect image data for two thermal infrared spectral bands with a spatial resolution of 120 m across a 185 km swath from the nominal 705 km Landsat altitude (Table 3). The two bands were selected to enable atmospheric correction of the thermal data using a split-window algorithm (Caselles et al., 1998) and represent an advancement over the single-band thermal data collected by previous Landsat satellites (the ETM + and TM sensors collect data for a 10.0–12.5 μm thermal band). The 120 m spatial resolution is a step back from the 60 m ETM + thermal band resolution and was specified as a compromise to the necessity of a rapid sensor development. The 120 m resolution is deemed sufficient for water consumption measurements over fields irrigated by center pivot systems (note that the instrument design exceeds requirements with a 100 m spatial resolution). These fields dot the U.S. Great Plains and many other areas across the world as circles 400 m to 800 m in diameter.

Table 3. TIRS spectral bands and spatial resolution (as built).

Band #

Center wavelength (μm)

Minimum lower band edge (μm)

Maximum upper band edge (μm)

Spatial resolution (m)

10

10.9

10.6

11.2

100

11

12.0

11.5

12.5

100

Like OLI, the TIRS requirements also specify cross-track spectral uniformity; radiometric performance including absolute calibration uncertainty, polarization sensitivity, and stability; ground sample distances and edge response; image geometry and geolocation including spectral band co-registration. The TIRS noise limits are specified in terms of noise-equivalent-change-in-temperature (NEΔT) rather than the signal-to-noise ratios used for OLI specifications (Table 4). The radiometric calibration uncertainty is specified to be less than 2% in terms of absolute, at-aperture spectral radiance for targets between 260 K and 330 K (less than 4% for targets between 240 K and 260 K and for targets between 330 K and 360 K).

Table 4. TIRS saturation radiance and noise-equivalent-change-in-temperature (NEΔT) specifications.

Band #

Saturation temperature

Saturation radiance

NEΔT at 240 K

NEΔT at 300 K

NEΔT at 360 K

10

360 K

20.5 W/m2 sr μm

0.80 K

0.4 K

0.27 K

11

360 K

17.8 W/m2 sr μm

0.71 K

0.4 K

0.29 K

A major difference between OLI and TIRS specifications is that TIRS requires only a three-year design life. This relaxation was specified to help expedite the TIRS development. The designers were able to save schedule through more selective redundancy in subsystem components rather than the more robust redundancy required for a five-year design life.

Excerpted from Remote Sensing of Environment 122, James R. Irons, John L. Dwyer, and Julia A. Barsi , The next Landsat satellite: The Landsat Data Continuity Mission, 11-21, Copyright 2012, doi:10.1016/j.rse.2011.08.026, with permission from Elsevier

Courtesy of the journal Remote Sensing of the Environment