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University of Nebraska–Lincoln



TM Band

Wavelength

Spectral Region

Target Reflectance

1

0.45-0.52

Blue-green

Separation of Soil &Vegetation

2

0.52-0.60

Green

Reflection from Vegetation

3

0.63-0.69

Red

Chlorophyll Absorption

4

0.76-0.90

Near-IR

Delineation of Water Bodies

5

1.55-1.75

Mid-IR

Vegetative Moisture

7

2.08-2.35

Mid-IR

Plant Heat Stress

6

10.4-12.5

Thermal

Hydrothermal Mapping

Landsat data can be used to interpret numerous phenomena. The interpretations are based on the spectral reflectance of the target. Spectral reflectance is the portion of the incident energy that is reflected. These spectral reflectance curves chart the reflectance of soil, vegetation, and water as a function of wavelength.

The fraction of energy reflected at a particular wavelength varies with different earth features, and the reflectance of each earth feature varies at different wavelengths. Thus, two features that are indistinguishable in one spectral range may be very different in another wavelength band.

Soil: Soil texture, surface roughness, and the presence of moisture, iron oxide, and organic matter can reduce soil reflectance in the visible region. Decreases in soil reflectance because of moisture are most notable in TM bands 5 and 7, which provide useful information for building construction and soil trafficability.

Vegetation: The spectral reflectance curve for healthy, green vegetation normally shows peaks and valleys. The reflectance in bands 1, 2, and 3 is indicated by pigments in plant leaves. Chlorophyll strongly absorbs energy in wavelengths of 0.45 and 0.67m. Healthy vegetation appears green because of the relatively high reflection of green energy by plant leaves and the high absorption of blue and red.

Reflectance in near-infrared Band 4 is determined by plant cell structure. In the mid-infrared bands 5 and 7, reflectance is due to plant water content.

A plant's spectral reflectance varies during its cycle of growth. The reflectance of a plant canopy depends upon the depth, density, age and diversity of the canopy.

Water: In the visible wavelengths, the energy reaching the sensor from a water body may be reflected from the surface of the water, from particulates in the water, or from the bottom if the water is clear and shallow. Water containing large quantities of suspended sediment normally has much higher reflectance than clear water in the same geographic area.

The three most common materials suspended in water are chlorophyll, tannin, and non-organic sediments. Because an increase in chlorophyll tends to decrease water reflectance in blue wavelengths and increase in green wavelengths, analysts can use Landsat TM data to monitor algae. Reflectance data can also be used to determine the presence of tannin dyes in bogs.

The visible bands provide information on water turgidity, bathymetry, currents and sediment plumes. Because water absorbs energy at infrared wavelengths, the infrared bands are used to easily locate and delineate water bodies.

Energy sensed with Band 6 is emitted, not reflected, from the earth's surface. Because it is not dependent on reflected sunlight, Band 6 imagery can be collected at night.

Since water is the only object whose emissivity is constant under different conditions, its temperature can be reliably estimated from it's radiance. Analysts often spot potential safety or environmental problems with Band 6 data by monitoring the water temperature of the cooling ponds and rivers near nuclear power plants.