Remote sensing is the science of obtaining information from a distance, using sensors that are not in physical contact with the object being observed. Remote sensing systems that monitor the earth’s surface rely on energy that is either diffusely reflected (scattered) or emitted from surface features. Using the Robin, for example, mounted on an Unmanned Aerial System (UAS), we are able to measure specific regions of reflected light that can tell us more about soils, plants, and water. It is possible to map field boundaries, locate stressed vegetation, and detect unusual conditions on farmers’ fields.
In reflected-light spectroscopy the fundamental property that we want to observe is spectral reflectance: the ratio of reflected energy (from the target) to incident energy as a function of wavelength. Reflectance varies with wavelength for most materials because energy at certain wavelengths is scattered or absorbed to different degrees. These reflectance variations are evident when we compare spectral reflectance curves (plots of reflectance versus wavelength) for different materials. The overall shape of a spectral curve and the position and strength of absorption bands can be used to identify and discriminate between different materials.
A multispectral sensor detects the radiation in a small number of wavelength bands of the same scene. Many multispectral systems use from three to six spectral bands in the visible to near infrared wavelength regions. Therefore, it is very important to define precisely the spectral bands positions; this allows us to use the appropriate algorithms to discriminate between different phenomena related to behavior of vegetation. The spatial, spectral, and temporal components of an image or set of images all provide information that we can use to interpret surface materials and conditions. For each of these components we can define the resolution of the images produced by the sensor system. These image resolution factors place limits on what information we can derive from remotely sensed images.