1) While ground spectrometers and sources can operate at a continuum of waveleng

Question

1) While ground spectrometers and sources can operate at a continuum of wavelengths (i.e hyperspectral), from space hyperspectral sensing is often quite hard. Most sensors are multispectral with a comparatively small number of bands.   As an example, consider LANDSAT Enhanced Thematic Mapper (ETM) which is the workhorse satellite for the USGS and helps map out the land properties over the entire globe. For this satellite, describe the main features including a) Channel Sensitivity b) Length of data record. Why is this sensor good for observing land but not very useful for oceans or atmosphere?

Explanation / Answer

The Enhanced Thematic Mapper of the Landsat 7 satellite is collecting land data since 1999. The main features of this satellite are:

Number of bands: 8

Types of channels: Thermal Infrared, Visible (blue. green, red), Near Infrared, Shortwave Infrared, Panchromatic

Channel Sensitivity: Thermal Infrared (10.4 -12.5 um), Blue (0.45 - 0.515 um), Red (0.63 - 0.69 um), Green (0.525 - 0.605 um), Near Infrared (0.775 - 0.9 um), Shortwave Infrared-I (1.55 - 1.75 um), Shortwave Infrared -II (2.08 - 2.35 um), Panchromatic (0.52 -0.9 um).

Length of the data record to date: 19 years

Since the multispectral-type ETM has a relatively lower spectral resolution in general, it is not very helpful in recording the sensitive information from clouds, gases, and aerosols but it can capture the differences in land-based features such as vegetation, biomass, soil moisture, and hydrothermal alterations in rocks. For obtaining the information related to ocean or atmosphere, the sensor needs to have a higher spectral resolution which is not the case with ETM.

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