The low reflection of ice and snow in the SWIR is related to their microscopic liquid water content. Reflectance decreases in the near infrared portion and there is very low reflectance in the SWIR (shortwave infrared). Ice and snow generally have high reflectance across all visible wavelengths, hence their bright white appearance. This is also true for waters containing high chlorophyll concentrations. Turbid water has a higher reflectance in the visible region than clear water. Water has high absorption and virtually no reflectance in near infrared wavelengths range and beyond. In its liquid state, water has relatively low reflectance, with clear water having the greatest reflectance in the blue portion of the visible part of the spectrum. As this internal structure varies amongst different plant species, the near infrared wavelengths can be used to discriminate between different plant species. This is primarily due to the internal structure of plant leaves. Healthy plants have a high reflectance in the near-infrared between 0.7 and 1.3 µm. Chlorophyll strongly absorbs light at wavelengths around 0.45 (blue) and 0.67 µm (red) and reflects strongly in green light, therefore our eyes perceive healthy vegetation as green. In general, healthy vegetation is a very good absorber of electromagnetic energy in the visible region. These signatures are visualized in spectral reflectance curves that show the percent reflectance as a function of wavelengths. These differences in reflectance make it possible to identify different earth surface features or materials by analyzing their spectral reflectance signatures. The reflectance of a material also varies with the wavelength of the electromagnetic energy. The reflectance properties of an object depend on the material and its physical and chemical state, the surface roughness as well as the geometric circumstances (e.g. Different surface features reflect or absorb the sun's electromagnetic radiation in different ways.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |