Remote sensing instruments for environmental observation
Remote sensing instruments for environmental observation on environmental satellites or weather satellites use the electromagnetic spectrum to study processes on the earth's surface or in the atmosphere. This is particularly useful if the collection and evaluation of data on the earth's surface is too complex to the required extent or the use of alternative methods, such as sound investigations, is not possible.
The instruments can basically be divided into two classes:
- Active instruments actively transmit radiation and pick up a reflected signal that has been modified by the properties of the observed object. From this signal and the assumed knowledge of the relationships ( model ) between the object and the sensor, the scientists can draw conclusions about the composition of the observed target. Examples are lidar and radar .
- Passive instruments detect the electromagnetic radiation that the object being observed emits. All objects are characterized by a characteristic emission of electromagnetic radiation . By measuring this radiation, scientists can draw conclusions about the state of the emitting object. For example, by measuring the intensity of the infrared light, conclusions can be drawn about the temperatures.
Further distinguishing features are the direction of observation, such as alignment directly under the satellites ( nadir mode) or tangential to the earth's surface ( limb mode), but also the wavelength of the radiation used . To observe the various processes in the atmosphere / biosphere of the earth , different wavelengths in the electromagnetic spectrum can be used differently depending on the area of application. The infrared wavelength range, the ultraviolet range or the microwave range are often used for this purpose .
In order to infer an atmospheric profile (vertical quantity distribution of a substance) from the measurement of a spectral signature, it is necessary to establish a relationship between the quantity distribution and the spectral signature. This can be achieved, for example, by applying and solving the radiation transport equation . Since this is often not possible analytically, one must use numerical methods for this .
The amount of data that arises in remote sensing is very large, so that the management of the data is a serious IT problem.