Applications of information collected by remote sensing
• - Conventional radar has been mainly associated with air traffic control, and with the collection of certain large-scale meteorological information. Doppler radar is used to support enforcement of local speed limits and also to support the collection of meteorological information such as wind speed and direction. Other types of active information collection include plasma "Plasma (state of matter)") from the ionosphere. Interferometric synthetic aperture radars are used to produce accurate digital models of large areas of terrain.
• - Laser and radar altimeters on satellites provide a large amount of information. By measuring the water bulges caused by gravity, they map features on the sea floor at a resolution of a mile or so. By measuring the height and length of waves in the ocean, altimeters measure wind speed and direction, and those of the ocean surface.
• - LIDAR (an acronym for Light Detection and Ranging) is known in the field of weapons range testing, such as laser-guided projectiles. LIDAR is used to detect and measure the concentration of various chemical agents in the atmosphere, while the skydiving branch LIDAR is used to measure heights of objects and features on the ground in a much more precise way than with any radar technology, with important applications in the field of hydrogeology, geomorphology and archaeology. Remote sensing of vegetation is one of the most relevant applications of LIDAR.
• - Radiometers and photometers are the most commonly used instruments, collecting emitted and reflected radiation in a wide spectrum of frequencies. (Visible range, infrared, microwave, gamma rays and sometimes ultraviolet). They can also be used to detect the emission spectrum of various chemical agents, thus providing information on the concentration of certain chemicals in the atmosphere.
• - Stereoscopic photography has often been used to make topographic maps by terrain analysts in “traffic” and in highway departments for potential routes.
• - Simultaneous multi-spectral platforms such as Landsat have been in use since the 1970s. These thematic mappers take images at multiple wavelengths of the electromagnetic spectrum and are typically found on Earth observation satellites, including (for example) the LandSat program or the IKONOS satellite. These maps can be used in mineral prospecting, detecting or monitoring land use, deforestation, the health status of indigenous plants and crops, including entire crop areas or forests.
• - In the spotlight against desertification, remote sensing allows you to follow and monitor risk areas in the long term, to determine desertification factors, to support decision-making regarding taking measures to manage the environment and evaluate the impact that these decisions may have.[2].
Geodesy.
• - Geodesy was first used in underwater aerial detection and in the collection of gravitational information used in military maps. This information revealed small perturbations in the Earth's gravitational field (geodesy) that could be used to determine changes in the distribution of mass on Earth, which could be used for future geological and hydrological studies.
Acoustic and semi-acoustic..
• - Passive: Sonar is used to detect, measure distances and measurements of objects under water and on land.
- Seismograms taken from different locations can locate and measure earthquakes after they occur by comparing the relative intensity and time at which they occurred.
• - Active: Pulses are used by geologists to detect oil deposits.
To coordinate a series of large-scale observations, most sensing systems depend on: platform location, time, rotation, and sensor orientation. Most current instruments typically use position information obtained from satellite navigation systems. Rotation and orientation are normally determined with an error of one or two degrees by electronic compasses. These compasses measure not only the azimuth, but also the altitude, since the lines of the Earth's magnetic field on Earth have a different curvature depending on the position you are in. If more exact orientations are desired, an Inertial Navigation System is required which is periodically realigned using different techniques, including taking stars as reference or important reference points.
The resolution has a fairly important impact on the collection of information; To understand it better: a lower resolution means less detail and greater coverage; A higher resolution, on the other hand, leads to greater detail but worse coverage. The ability to determine the appropriate resolution at all times results in better results and also prevents the collapse of the storage and transmission units (a higher resolution implies a larger size).
Information processing
Remote sensing, if we speak in a general way, works following the principle of the inverse problem. While the object or phenomenon in question (the state) is not going to be measured directly, there are other variables that are detected and measured (the observation), which are intrinsically related to the object of interest, through a computer-created model. An analogy to understand this is trying to determine the type of animal by its footprints. For example, since it is impossible to directly measure the temperature in the upper layers of the atmosphere, it is possible to measure the emissions of a certain spectrum of known chemical species (CO2) in that region. The frequency of said emission can be related to the temperature of that area through several thermodynamic relationships.
The quality of the information collected remotely depends on its spatial, spectral, radiometric and temporal resolutions.
Spatial resolution.
It is the size of a pixel that is saved in a raster image – pixels correspond to square areas whose size varies from 1 to 1000 meters.
Spectral resolution.
It is the amplitude of the wavelength of the different recorded frequencies – normally, it is related to the number of frequencies that the platform records. The latest Landsat fleet, "Landsat 8", comprises 11 different bands including several in the infrared spectrum; in total it acquires from 0.43 μm to 12.51 μm.[3] The Hyperion sensor on the “Earth Observing-1” manages 220 bands ranging from 0.4 μm to 2.5 μm, with a spectral resolution of 0.10 to 0.11 μm per band collected.
Radiometric resolution.
It is the ability of the sensor to distinguish different intensities of radiation. It normally comprises 8 to 14 bits, corresponding to the 256 levels of a gray scale, and can reach 16,384 color intensities in each band. It also depends on the noise of the device "Noise (sound)").
Temporary resolution.
It is the frequency with which the plane or satellite flies over an area, and is only important in studies to investigate the effect of the passage of time, such as in monitoring deforestation. The passage of a cloud over the area or object would make it necessary to repeat the process over that area.
In order to create maps based on the information collected by a sensor, most remote sensing systems extrapolate the information extracted by the sensor in relation to a reference point, including distances between known points on the ground. This all depends on the type of sensor used. For example, in ordinary photographs, the distances are most precise in the center of the image, which become distorted as you move away from the center of it. Another important factor is the roller against which the photos are placed, a fact that can cause serious errors in the photographs when they are used to measure distances. This is solved by georeferencing, which involves computer assistance in relating points in the image (30 or more per image) that are extrapolated using a previously established reference point, “transforming” the image to produce more precise spatial information. In the early 1990s, most satellite images sold were fully georeferenced. Apart from this correction, images may require radiometric and atmospheric correction.