Remote sensing

Remote sensing, or remote sensing, is the acquisition of information on a small or large scale about an object or phenomenon, either using wireless or non-wireless real-time recording or scanning instruments. are in direct contact with the object (such as planes, satellites, spacecraft, buoys, or ships). In practice, remote sensing consists of collecting information through different devices from a specific object or area. For example, Earth observation or weather satellites, ocean and atmospheric buoys, magnetic resonance imaging (MRI), positron emission tomography (PET), X-rays, and space probes are all examples of remote sensing. Currently, the term refers in a specific way to the use of sensor technologies for image acquisition, including: instruments aboard satellites or airborne, uses in electrophysiology, and differs in other fields related to images such as medical imaging.

There are two main kinds of remote sensing: passive remote sensing and active remote sensing:

• Passive teledetctors detect natural radiation emitted or reflected by the surrounding object or area being observed. The reflected sunlight is one of the most common types of radiation measured by this kind of remote sensing. Some examples can be photography, infrareds, CCD sensors (charge-coupled devices, “interconnected electrical load device”) and radiometers.

• Active teledetctors on the other hand emit energy to scan objects and areas with which the teledetector measures the radiation reflected from the target. A radar is an example of an active teledetector, which measures the time it takes to go and return from a point, thus establishing the location, height, speed and direction of a given object.

Remote sensing makes it possible to collect information from dangerous or inaccessible areas. Some applications may be monitoring deforestation in areas such as the Amazon basin, the effect of climate change on glaciers and in the Arctic and Antarctic, and in-depth sounding of oceanic fault lines and coasts. The military collective, during the Cold War, made use of this technique to collect information on potentially dangerous borders. Remote sensing also replaces the slow and costly collection of information on the ground, also ensuring that the areas or objects analyzed are not altered in the process.

Orbital platforms can transmit information from various bands of the electromagnetic spectrum that, in collaboration with aerial or terrestrial sensors and a joint analysis, provide researchers with enough information to monitor the evolution of natural phenomena such as El Niño. Other uses encompass areas such as Earth sciences, specifically natural resource management, agricultural fields in terms of use and conservation, and national security.

Information Acquisition Techniques

Multispectral acquisition is based on the collection and analysis of areas or objects that emit or reflect radiation at a higher level than the surrounding objects.

Applications of the information collected by remote sensing

• Conventional radar has mainly been associated with air traffic control, and the collection of some large-scale weather information. Doppler radar is used as support to enforce local speed limits and also as a reinforcement to the collection of weather information such as wind speed and direction. Other types of active information collection include ionosphere plasma. Synthetic opening interferometric radars (Interferometric synthetic aperture radar) are used to produce accurate digital models of large terrain areas.
• Laser and radar altimeters on satellites provide a lot of information. By measuring the water protuberances caused by gravity, they map the characteristics at the bottom of the sea in a resolution of a mile more or less. Measuring the height and length of the waves in the ocean, the altimeters measure the speed of the wind and direction, and the surface of the ocean.
• LIDAR (an English acronym Light Detection and Ranging) is known in the range of weapons tests, as in laser-guided projectiles. LIDAR is used to detect and measure the concentration of several chemical agents in the atmosphere, while the LIDAR parachuting branch is used to measure heights of objects and characteristics on the earth in a much more precise way than with any radar technology, with important applications in the field of hydrogeology, geomorphology and archaeology. Remote vegetation remote sensing is one of the most relevant LIDAR applications.
• Radiometers and photometers are the most commonly used instruments, collecting radiation emitted and reflected in a wide spectrum of frequencies. (Visible strip, infrared, microwave, gamma rays and sometimes ultraviolet). They can also be used to detect the emission spectrum of several chemicals, thus providing information on the concentration of certain chemicals in the atmosphere.
• Stereoscopic photography has often been used to make topographic maps by ground analysts in “traffability” and in road departments for potential routes.
• Simultaneous multi-spectral platforms like Landsat have been in use since the 1970s. These thematic mapers take images in multiple wavelengths of the electromagnetic spectrum and are normally found in terrestrial observation satellites, including (e.g.) the LandSat program or the IKONOS satellite. These maps can be used in mineral surveying, detecting or monitoring land use, deforestation, the state of health of indigenous plants and crops, including whole areas of cultivation or forests.
• At the point of view against desertification, remote remote remote sensing allows to monitor and monitor long-term risk areas, to identify desertification factors, to support decision-making in order to take measures to manage the environment and to assess the impact that such decisions may have.

Geodesy

• Geodesy was first used in underwater air detection and in the collection of gravitational information used on military maps. This information revealed small disturbances in the gravitational field of the Earth (geodesia) that could be used to determine changes in the distribution of the mass on Earth, which could be used for future geological and hydrological studies.

Acoustic and semi-acoustic.

• Passive: The Soar is used to detect, measure distances and measurements of objects under water and earth.
  • The collected sismograms of different places can locate and measure earthquakes after they occur by comparing the relative intensity and time they occurred.
• Activate: Pulses are used by geologists to detect oil deposits.

To coordinate a series of large-scale observations, most detection systems rely on: platform location, time, rotation, and sensor orientation. Newer instruments normally use position information obtained from satellite navigation systems. Rotation and orientation are normally determined to within one or two degrees by electronic compasses. These compasses measure not only the azimuth, but also the altitude, since the Earth's magnetic field lines have a different curvature depending on the position in which you are. If more exact orientations are desired, an Inertial Navigation System is required which is periodically realigned using different techniques, including taking stars as references or important reference points.

Resolution has a fairly significant impact on information gathering; to understand it better: lower resolution means less detail and more coverage; on the contrary, a higher resolution entails a greater detail but a worse coverage. The ability to determine the appropriate resolution at all times results in better results and also prevents the collapse of storage and transmission units (higher resolution means 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) will not 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 model created By computer. An analogy to understand this is trying to determine the type of animal by its footprints. Thus, 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 various thermodynamic relationships.

The quality of the information collected at a distance depends on its spatial, spectral, radiometric and temporal resolutions.

Spatial resolution

This is the size of a pixel that is stored in a raster image – pixels correspond to square areas ranging in size from 1 to 1000 meters.

Spectral resolution

This is the amplitude of the wavelength of the different frequencies recorded – usually related to the number of frequencies the platform records. The latest Landsat fleet, "Landsat 8", comprises 11 different bands including several from the infrared spectrum; in total it acquires from 0.43 μm to 12.51 μm. 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.

Temporal resolution

It is the frequency with which the plane or satellite flies over an area, and it 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, what most remote sensing systems do is extrapolate the information extracted by the sensor in relation to a reference point, including distances between known points in the land. This all depends on the type of sensor used. For example, in ordinary photographs, distances are most accurate in the center of the image, which become distorted as you move away from the center of the image. 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 help to relate points on the image (30 or more per image) that are extrapolated using a previously established reference point, “transforming” the image to produce more accurate spatial information. In the early 1990s, most satellite images sold were fully georeferenced. Apart from this correction, the images may need radiometric and atmospheric correction.

Radiometric correction

Gives a scale of values per pixel. For example, the monochrome scale from 0 to 255 will be converted to actual radiation values.

Atmospheric correction

Removes atmospheric “haze” by rescaling each frequency band to its minimum value (each pixel to 0). The digitization of information also makes it possible to manipulate data by changing values in the gray scale.

Interpretation is the critical part of the process of making information understandable. The first application of this was in aerial photography, which used the following process: spatial measurements with the use of an illuminated table in both simple conventional and stereographic coverage. Make use of the known dimensions of objects to detect modifications. Image analysis is a computer-automated application that is being used more and more every day.

Object-Based Image Analysis (OBIA) is a subdiscipline of GIScience dedicated to partitioning remote sensing images into meaningful images of objects, and evaluating their features on special temporal and spectral scales.

Old data obtained from remote sensing is often valuable because it provides long-term information over a large geographic portion. At the same time, the information is often complex to interpret and difficult to store. Today's systems tend to store everything digitally, usually without loss of compression. The tricky thing about all this is that the information is fragile and its format can be archaic and difficult to interpret, as well as being easy to falsify. One of the best systems for storing information is on microfilm. Microfilms normally survive in ordinary libraries, with a life span of several centuries. They can be created, copied, archived and collected by automated systems. They are as compact as information stored on magnetic devices and can still be read by humans with a minimum of suitable equipment.

Levels of information processing

To ease the information processing dilemma, various levels of processing were defined in 1986 by NASA as part of its Earth Observing System and were adopted by both NASA (for example,) and the other places (for example,). These definitions are:

Saving the information from Level 1 is essential (it is the most reversible level among other things) since it has a scientific meaning and an important utility, and is the basis for the generation of the rest of the levels. Level 2 is the first level directly usable by most scientific applications; its value is much greater than that of the rest of the lower levels. Level 2 tends to be less heavy than Level 1 since its parameters have been reduced, either temporally, spatially, or spectrally. Level 3 is already much smaller than the rest and can be manipulated without fear of mishandling the data. This information is usually more general and useful for most applications. The temporal and spatial organization of level 3 makes it possible to combine information from other sources.

History

The TR-1 The TR-1 reconnaissance/vigilance aircraft.

La Mars Odyssey 2001 used spectrometers and "imagers" to capture evidence of the existence of water or volcanic activity in Mars.

Beyond the primitive methods used by our ancestors (climbing a cliff or a tree to see the landscape), the modern discipline emerged with the invention of flight. G. Tournachon (aka Nadar), a well-known balloon pilot, took photographs of Paris from his balloon in 1858. Homing pigeons, kites, rockets, and unmanned balloons were also used to take images. With the exception of the globes, these early images were not very useful for mapping or any scientific research.

Systematic aerial photography was developed by the military for surveillance and reconnaissance purposes in World War I, and reached its climax during the Cold War with the use of modified fighter aircraft such as the P- 51, the P-38, the RB-66 and the F-4C, or some intelligence gathering platforms such as the U2/TR-1, the SR-71, the A-5 and the OV-1. Methods were then developed to create sensors smaller than those used by law enforcement and the military, both on manned and unmanned platforms.

The advantage of this is that it requires minimal modification to a given airplane. Later imaging technology included infrared, conventional imaging, Doppler, and synthetic aperture radars.

The development of artificial satellites as early as the second half of the 20th century allowed the use of remote sensing to progress to global scale and end the Cold War. The instruments on board various ground observers and meteorological platforms such as Landsat, Nimbus and some more recent ones such as RADARSAT and UARS provided global measures of information of various types (civil, military and research). Space probes to other planets have also provided the opportunity to conduct remote sensing study of extraterrestrial environments; the synthetic aperture radar aboard Magellan provided detailed topographic maps of Venus, while instruments aboard SOHO enabled studies of the Sun and solar winds.

Recent research includes, in the early 1960s and 1970s, the development of image processing from satellite images. Several research teams in Silicon Valley including NASA Ames Research Center, GTE, and ESL Inc. have developed techniques for using the Fourier Transform as a way to enhance image information.

The introduction of online Web services for rapid access to remote sensing information in the XXI century (mainly images low or medium resolution), such as Google Earth, has made remote sensing familiar to the general public and popular in the world of science.

Remote Sensing Software

The information collected by remote sensing is processed and analyzed by computer programs.

A large number of open source and paid applications to process this kind of information. According to the NOAA study conducted by Global Marketing Insights, Inc., the most remote sensing-related applications among Asian academies are: ESRI 30%, ERDAS IMAGINE 25%, ITT Visual Information Solutions (ENVI) with 17%, MapInfo with 17% and ERMapper with 11%. Among Western academies, the study found these other percentages: ESRI 39%, ERDAS IMAGINE 27%, MapInfo 9%, AutoDesk 7% and ENVI 17%. Other remote sensing related application suites include PCI Gemoatics developed by PCI Geomatica, a leading remote sensing related suite of applications in Canada, IDRISI from Clark Laboratories, and eCognition software from Definiens. Some open source applications are: GRASS GIS, QGIS, ILWIS, Optics, SPRING and Orfeo toolbox.

Recommended reading

• Campbell, J.B. (2002). Introduction to remote sensing (3rd edition). The Guilford Press.
• Jensen, J.R. (2007). Remote sensing of the environment: an Earth resource perspective (second edition). Prentice Hall.
• Jensen, J.R. (2005). Digital Image Processing: a Remote Sensing Perspective (3rd edition). Prentice Hall.
• Lentile, Leigh B.; Holden, Zachary A.; Smith, Alistair M. S.; Falkowski, Michael J.; Hudak, Andrew T.; Morgan, Penelope; Lewis, Sarah A.; Gessler, Paul E.; Benson, Nate C. (2006). Remote sensing techniques to assess active fire characteristics and post-fire effects 3 (15). International Journal of Wildland Fire. pp. 319-345. Archived from the original on August 12, 2014. Consultation on 25 April 2010.
• Lillesand, T.M.; R.W. Kiefer, and J.W. Chipman (2003). Remote sensing and image interpretation (5th edition). Wiley. The reference uses the obsolete parameter |coautores= (help)
• Richards, J.A.; and X. Jia (2006). Remote sensing digital image analysis: an introduction (4th edition). Springer. The reference uses the obsolete parameter |coautores= (help)
• Mallorquí, Jordi J.; Blanco, P.; Navarrete, D.; Duque, S. (2006). Advances on DInSAR with ERS and ENVISAT Data using the Coherent Pixels Technique (CPT). IGARSS 2006.
• Lasaponara, Rosa; Nicola Masini (2012). Satellite Remote Sensing - A new tool for Archaeology. Remote Sensing and Digital Image Processing Series, Volume 16, 364 pp., ISBN 978-90-481-8801-7. The reference uses the obsolete parameter |coautores= (help)