Difference between revisions of "Remote sensing"

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==Introduction==
 
==Introduction==
−
[[Image:Swarm_over_Italy.jpg|thumb|right|200px|<small>Use of satellites as remote sensing platforms (Photo credit: ESA-AOES Medialab)</small>]]
+
 
−
<P ALIGN="justify">There is an increasing demand for accurate, timely information on environmental and natural resources, including spatial relationships and temporal changes and trends, local to global. In the broadest sense, '''remote sensing''' is the measurement or acquisition of information of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object. In practice, remote sensing is the utilization at a '''distance''' (as from aircraft, spacecraft, satellite, or ship) of any device for gathering information about the environment.</P>
+
[[Image:Swarm_over_Italy.jpg|thumb|right|300px| <small> '''Fig. 1.''' Use of satellites as remote sensing platforms (Photo credit: ESA-AOES Medialab).</small>]]
 +
 
 +
There is an increasing demand for accurate, timely information on natural resources and ecosystems, their spatial distribution and temporal changes and trends, from local to global. In the broadest sense, remote sensing is the measurement or acquisition of information about an object or phenomenon by a sensor that is not in direct physical contact with the object. Information is conveyed by waves radiating from the object. The sensor is mounted on a fixed frame (a mast) or on a moving platform, for example an aircraft, drone, satellite or a frame towed behind a ship.
 +
 
 
Advantages of this technology are:
 
Advantages of this technology are:
−
*Observation of a large geographical area
+
*Observation of a large geographical area (from aircraft or satellite  - Fig. 1)
−
*Long-term and fast collection of data
+
*Long-term and fast collection of data (from satellite)
−
*Lower collecting costs
+
*Low collecting costs
 
*"Inaccessible" regions become accessible (e.g. Antarctica)
 
*"Inaccessible" regions become accessible (e.g. Antarctica)
−
*Object is not being destroyed
+
*Object is not being perturbed or destroyed
 
Disadvantages are:
 
Disadvantages are:
−
*Lower spatial resolution (depending on the type of sensor)
+
*Lower spatial resolution than in situ measurement (depending on the type of platform or  sensor)
−
*Need for the installation of complex systems (which have a long testing phase)
+
*Initial investment in development and installation
−
*Captured data need to be calibrated via in-situ data
+
*Collected data need to be calibrated via in-situ data
 
*Noise caused by another source than the desired one
 
*Noise caused by another source than the desired one
 
*Atmospheric effects degrade the quality of the images and need to be corrected
 
*Atmospheric effects degrade the quality of the images and need to be corrected
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==Brief history==
 
==Brief history==
  
−
{|border="1" align=center cellspacing="0" cellpadding = "8" width="800px"  
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{|border="1" align=center cellspacing="0" cellpadding = "8" width="800px" style="font-size:80%"
 
|-
 
|-
−
!style="background-color:#398C9D" text-align="center"|'''<1960'''
+
| 1826 || Invention of photography by Joseph Nicéphore Niépce
−
!style="background-color:#398C9D" text-align="center"| '''Aerial photography'''
+
|-  
 +
| 1850s || Photography with cameras from hot-air balloons
 
|-
 
|-
−
| 1826
+
| 1903 || Invention of pigeon photography (used during World War I and the Civil War)
−
| Invention of photography by Joseph Nicéphore Niépce
+
|-
−
|-  
+
| 1904 || Invention 'telemobiloscope', first radar-type device by Christian Hülsmeyer
−
| 1850s
+
|-
−
| Photography with cameras from hot-air balloons
+
| 1909 || Photography from air planes
 +
|-
 +
| 1913 || First acoustic underwater transducer patented by Reginald A. Fessenden, precursor of the sonar (sound navigation and ranging).
 +
|-
 +
| World War I  || Military surveillance: airplanes with cameras
 
|-
 
|-
−
| 1903
+
| 1920 || First detailed seafloor maps using sonar by the US Coast and Geodetic Survey.
−
| Invention of pigeon photography (used during World War I and the Civil War)
 
 
|-
 
|-
−
| 1909
+
| 1922 || Borehole radar using pulsed modulation patented by Loewy
−
| Photography from air planes
 
 
|-
 
|-
−
| World War I
+
| 1930  || Invention of Lidar (acronym of "light detection and ranging" or "laser imaging, detection, and ranging") by E. H. Synge
−
| Military surveillance: airplanes with cameras
 
 
|-
 
|-
−
| style="background-color:#398C9D" text-align="center"; |'''From 1960'''
+
| 1942 || First ship radars for the fleets of the U.S. and British navy
−
| style="background-color:#398C9D" text-align="center";|'''Shift in the use of platforms for remote sensing: air planes are replaced by satellites'''
 
 
|-
 
|-
−
| 1960s
+
| 1960s || Space programs and race between the United States (US) and the Soviet-Union (USSR)
−
| Space programs and race between the United States (US) and the Soviet-Union (USSR)
 
 
|-
 
|-
−
| 04 October 1957
+
| 04 October 1957 || Sputnik I (USSR): first artificial satellite to go into orbit
−
| Sputnik I (USSR): first artificial satellite to go into orbit
 
 
|-
 
|-
−
| 31 January 1958
+
| 31 January 1958 || Explorer I (US) is launched
−
| Explorer I (US) is launched
 
 
|-
 
|-
 
| 1960
 
| 1960
−
| TIROS-1: first meteorological satellite  
+
| TIROS-1: first meteorological satellite. First use of term 'Remote sensing'
−
First use of term 'Remote sensing'
+
|-
 +
| 1961 || First Lidar system developed by the Hughes Aircraft Company
 
|-
 
|-
−
| 1972
+
| 1964 || First application of marine X-band (or microwave) radar for ocean wave imaging by Ijima et al. (1964<ref>Ijima, T., Takahashi, T. and Sasaki, H. 1964. Application of radars to wave observations. Proc. 11th Int. Conf. Coastal Engineering 30: 10-22</ref>)
−
| Landsat-1: launch of the first earth resource satellite
 
 
|-
 
|-
−
| 1990s
+
| 1972 || Landsat-1: launch of the first earth resource satellite
−
| Launch of earth resource satellites by national space agencies and commercial companies
+
|-
 +
| 1990s || Launch of earth resource satellites by national space agencies and commercial companies
 
|-
 
|-
 
|}
 
|}
 
<br style="clear:both;"/>
 
<br style="clear:both;"/>
 +
  
 
==General principles of remote sensing==
 
==General principles of remote sensing==
−
<P ALIGN="justify">Remote [[sensors]] are devices that measure and record specific types of energy. In remote sensing this energy is electromagnetic radiation which is reflected or emitted by all natural and synthetic objects on Earth. The '''electromagnetic spectrum''' is the continuous range of electromagnetic radiation. The spectrum can be divided in the following regions: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves. Remote sensing involves measurement of energy in many parts in the EM spectrum and takes place in spectral bands. A spectral band is defined as a discrete interval of the EM spectrum. Satellite sensors for example have been designed to measure responses within particular spectral bands to enable the discrimination of the major Earth surface materials. Scientist choose a particular spectral band for data collection depending on what they wish to examine. The data captured and recorded by the sensors must be analyzed by interpretive and measurement techniques in order to provide useful information about their subjects. The technique varies from simple traditional methods of visual interpretation to complicated methods using computer processing. The output is usually an image.</P>
+
Remote sensors are devices that measure and record specific types of energy. This energy is electromagnetic radiation in remote sensing via the air; underwater remote sensing usually involves acoustic waves. The electromagnetic spectrum is the distribution of radiation energy over wavelengths. The spectrum can be divided into different spectral ranges: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves (Fig. 2). Remote sensing involves measuring energy in spectral bands - discrete intervals of the EM spectrum. Satellite sensors are designed to measure signals emitted by objects on the Earth's surface within certain spectral bands from which the characteristics of these objects can be inferred. Scientists choose a particular spectral band for data collection depending on what they want to investigate. The data recorded by the sensors must be pre-processed (corrected, enhanced), analyzed (classified) and interpreted to provide useful information. Simple traditional methods of visual interpretation have evolved into advanced mathematical and statistical methods using models and analysis techniques as described in [[Data analysis techniques for the coastal zone]] and many other articles in the Coastal Wiki.  
−
[[Image:EM.png|thumb|center|800px|<small>The electromagnetic spectrum (Photo credit: Johannes Ahlmann)</small>]]
+
 
 +
 
 +
[[Image:EM.png|thumb|center|800px|<small>'''Fig. 2.''' The electromagnetic spectrum (Photo credit: Johannes Ahlmann). </small>]]
 +
 
  
 
== Types of sensors==
 
== Types of sensors==
−
<P ALIGN="justify">Remote sensing systems can be divided into 2 categories: '''active''' or '''passive''' sensors. In active sensors (e.g. radar) energy is transmitted from the sensor so they provide their own energy source for illumination. The sensor emits radiation which is directed toward the object or surface to be investigated. The radiation reflected from that target is detected and measured by the sensor. Passive systems (e.g. photographic camera) measure energy that is naturally available or depend on an external energy source (for example the sunlight).</P>
+
Remote sensing systems can be divided into 2 categories: '''active''' and '''passive''' sensors. Active sensors (usually detection and ranging systems such as radar, sonar, Lidar) emit radiation which is directed toward the object or surface to be investigated. The radiation emitted by an active sensor provides a specific spectral energy pulse to the study object that activates a response signal which is detected, measured and timed by the sensor. It thus allows to determine distances (ranges). Passive systems (e.g. photographic camera) record the radiation emitted by an object that receives radiation (energy) from an external energy source (for example the sunlight). The radiation emitted by an object is due to reflection, backscatter (diffuse) and re-emitted back radiation. It can provide information about the shape (via reflected radiation), pattern, type of substance and composition of the object.
 +
 
 +
 
 +
[[Image:Phytoplankton_1.jpg|thumb|400px|left|<small>'''Fig. 3''' The basic principle of ocean colour remote sensing: The radiance, which arrives at the satellite consists of 4 components: (1) radiance which is scattered in the atmosphere, (2) radiance which is specularly reflected at the sea surface, (3) radiance which is backscattered by water and its constituents and (4) in shallow water, radiance, which is reflected from the sea bottom. All 3, or in case of shallow water 4, components have to be determined to retrieve the radiance leaving the water, i.e. component 2.</small>]]
  
 
== Atmospheric effects==
 
== Atmospheric effects==
−
<P ALIGN="justify">
+
Remote sensors that observe the Earth are looking through the atmosphere. The atmospheric constituents (particles and gases) can affect the incoming light and radiation by causing wavelength-dependent '''absorption''' and '''scattering''' (Fig. 3). '''Scattering''' occurs when particles or large gas molecules present in the atmosphere interact with the electromagnetic radiation and cause it to be diverted from its original path. '''Absorption''' causes molecules in the atmosphere to absorb and re-emit energy at various wavelengths. Ozone, carbon dioxide and water vapor are the most important atmospheric constituents that absorb radiation.
−
When the Earth is observed remote sensors are looking through the atmosphere. The atmospheric constituents (particles and gases) can affect the incoming light and radiation by causing wavelength dependent '''absorption''' and '''scattering'''. '''Scattering''' occurs when particles or large gas molecules present in the atmosphere interact with and cause the electromagnetic radiation to be redirected from its original path. '''Absorption''' causes molecules in the atmosphere to absorb energy at various wavelengths. Ozone, carbon dioxide and water vapor are the most important to absorb radiation.
+
These atmospheric effects degrade the quality of the images. They need to be corrected for before the images are subjected to further analysis and interpretation.
−
These atmospheric effects degrade the quality of the images. Some of them can be corrected before the images are subjected to further analysis and interpretation.</P>
+
[[Sunglint]], the direct reflection of the sun from the water surface to the sensor, is another effect that must be corrected for.
 +
<br clear=all>
 +
 
 +
== Remote sensing applications in the Coastal Wiki==
 +
*Plankton, algae: [[Plankton remote sensing]], [[Plankton remote sensing North Sea]], [[Remote sensing of zooplankton]], [[The Baltic Algae Watch System - a remote sensing application for monitoring cyanobacterial blooms in the Baltic Sea]]
 +
*Habitats: [[Use of Lidar for coastal habitat mapping]], [[Tidal flats from space]], [[The HIMOM and OFEW approaches to monitoring intertidal flats]], [[Acoustic kelp bed mapping in shallow rocky coasts - case study Helgoland (North Sea)]], [[Application and use of underwater video]]
 +
*Animals: [[Acoustic monitoring of marine mammals]]
 +
*Suspended sediment: [[Optical Laser diffraction instruments (LISST)]], [[Optical backscatter point sensor (OBS)]], [[Acoustic backscatter profiling sensors (ABS)]]
 +
*Pollution: [[Oil spill monitoring]]
 +
*Sea surface elevation (satellite altimetry): [[Space geodetic techniques for coastal zone monitoring]]
 +
*Bathymetry: [[Satellite-derived nearshore bathymetry]], [[Bathymetry from remote sensing wave propagation]], [[HyMap: Hyperspectral seafloor mapping and direct bathymetry calculation in littoral zones]], [[Bathymetry German Bight from X-band radar]], [[Monitoring coastal morphodynamics using high-precision multibeam technology]], [[Instruments for bed level detection]], [[Argus applications]]
 +
*Shoreline: [[Use of aerial photographs for shoreline position and mapping applications]]
 +
*Waves: [[Waves and currents by X-band radar]], [[Measuring instruments for fluid velocity, pressure and wave height]]
 +
*Currents: [[Measuring current fields in the German Bight by radar techniques]], [[Application of radar hydrography in the German Wadden Sea]], [[Acoustic point sensors (ASTM, UHCM, ADV)]], [[Currents and turbulence by acoustic methods]]
 +
*Wind: [[WiRAR - A marine radar wind sensor]], [[WiSAR - Wind retrieval from synthetic aperture radar]]
 +
 
 +
 
 +
==Articles related to remote sensing==
 +
 
 +
===Satellite remote sensing===
 +
:[[Light fields and optics in coastal waters]]
 +
:[[Optical remote sensing]]
 +
:[[Plankton remote sensing]]
 +
:[[Plankton remote sensing North Sea]]
 +
:[[Satellite-derived nearshore bathymetry]]
 +
:[[Oil spill monitoring]]
 +
:[[Use of Lidar for coastal habitat mapping]]
 +
:[[HyMap: Hyperspectral seafloor mapping and direct bathymetry calculation in littoral zones]]
 +
:[[Plankton remote sensing]]
 +
:[[Remote sensing of zooplankton]]
 +
:[[The Baltic Algae Watch System - a remote sensing application for monitoring cyanobacterial blooms in the Baltic Sea]]
 +
:[[Bathymetry from remote sensing wave propagation]]
 +
:[[Use of aerial photographs for shoreline position and mapping applications]]
 +
:[[SeaWiFS]]
 +
:[[MODIS]]
 +
:[[MERIS]]
 +
:[[Tidal flats from space]]
 +
:[[Detecting the unknown - novelty detection of exceptional water reflectance spectra]]
 +
:[[The HIMOM and OFEW approaches to monitoring intertidal flats]]
 +
 
 +
===Radar remote sensing===
 +
:[[Coastal ocean satellite altimetry]]
 +
:[[Waves and currents by X-band radar]]
 +
:[[Bathymetry German Bight from X-band radar]]
 +
:[[Measuring current fields in the German Bight by radar techniques]]
 +
:[[Application of radar hydrography in the German Wadden Sea]]
 +
:[[WiRAR - A marine radar wind sensor]]
 +
:[[WiSAR - Wind retrieval from synthetic aperture radar]]
 +
 
 +
===Under water remote sensing===
 +
:[[General principles of optical and acoustical instruments]]
 +
:[[Monitoring coastal morphodynamics using high-precision multibeam technology]]
 +
:[[Optical Laser diffraction instruments (LISST)]]
 +
:[[Remote sensing of zooplankton]]
 +
:[[Optical backscatter point sensor (OBS)]]
 +
:[[Instruments and sensors to measure environmental parameters]]
 +
:[[Acoustic monitoring of marine mammals]]
 +
:[[Acoustic point sensors (ASTM, UHCM, ADV)]]
 +
:[[Acoustic backscatter profiling sensors (ABS)]]
 +
:[[Currents and turbulence by acoustic methods]]
 +
:[[Acoustic kelp bed mapping in shallow rocky coasts - case study Helgoland (North Sea)]]
 +
:[[Instruments for bed level detection]]
 +
:[[Measuring instruments for fluid velocity, pressure and wave height]]
 +
 
 +
===Video camera===
 +
:[[Argus video monitoring system]]
 +
:[[Argus video]]
 +
:[[Underwater video systems]]
 +
:[[Video technology]]
 +
:[[Application and use of underwater video]]
 +
:[[Argus applications]]
  
−
== Remote sensing applications==
 
−
* Agriculture
 
−
* Environmental monitoring and risks
 
−
* Geology
 
−
* Oceanography
 
−
* Climatology
 
−
* Ecology
 
−
* Meteorology
 
−
* Topography and cartography
 
−
* Oil and mineral exploitations
 
−
* Military
 
−
== Eutrophication, ocean colour and algal blooms==
 
−
[[Image:Envisatsummerbloom.png|300px|thumb|right|<small>Earth-observing satellite Envisat MERIS image of a phytoplankton bloom in the South Atlantic Ocean: different types and quantities of phytoplankton exhibit different colours, such as the blues and greens in this image)(Photo Credit: ESA) </small>]]
 
−
<P ALIGN="justify">The main reason to measure ocean colour is to study [[phytoplankton]], the microscopic algae which are at the base of the oceanic food web. Remote sensing plays an important role in the detection, monitoring and prediction of [[Algal_bloom|algal blooms]] in the marine environment as these algae are considered a potential threat when they form so called [[Harmful_algal_bloom|harmful algal blooms]] and so appropriate measures can be taken. In situ measurements are useful when more information is required on the type of algae present but when there is a sudden shift in time and location these methods become too expensive.
 
−
Satellite sensors detect the reflected light by the sea surface in different wavelengths. The "colour" of the ocean is determined by the impact of light with the water and any colored particles or dissolved chemicals in the water. Colour is the light reflected by the water and the substances present in it. When light hits a water molecule or a coloured substrate in it, the different colours (wavelengths) can be absorbed or scattered in differing intensities. The colour we see results from the colours that are reflected. The substances in seawater which most affect the water colour are: [[phytoplankton]], inorganic particles, dissolved organic chemicals, and the water molecules themselves. [[Phytoplankton]] contains green-coloured chlorophyll-a (necessary to produce organic carbon using light and carbon dioxide during [[photosynthesis]]) which absorbs red and blue light and reflects green light. The ocean colour is also an indicator of the health of oceans. The chlorophyll concentrations can be derived from satellite data by calculating the ratio blue / green of the ocean. When blue is more absorbed, green is more reflected which indicates a higher concentration of phytoplankton in the water and vice versa. Remote sensing can thus provide a wide visual picture and allows us to create more insight into the eutrophication processes.</P>
 
−
<P ALIGN="justify">Examples of modern colour satellites sensors are [[SeaWiFS]] (Sea-viewing Wide Field of view Sensor), [[MODIS]] (Moderate Resolution Imaging Spectroradiometer) and [[MERIS]] (Medium Resolution Imaging Spectrometer). Once a bloom begins, an ocean colour sensor can make an initial identification of its chlorophyll pigment, and therefore its species and toxicity. An overview of satellites and sensors used in Earth Observation is found [http://eoedu.belspo.be/en/satellites/index.htm here].</P>
 
  
−
==See also==
+
{{2Authors
−
* [[Optical remote sensing]]
+
|AuthorID1=26102
−
*[[Real-time algae monitoring]]
+
|AuthorFullName1= Knockaert, Carolien
 +
|AuthorName1=Carolienk
 +
|AuthorID2=120
 +
|AuthorFullName2=Job Dronkers
 +
|AuthorName2=Dronkers J
 +
}}
  
−
==References==
+
[[Category:Coastal and marine observation and monitoring]]
−
<P ALIGN="justify">
 
−
#Natural resources Canada: Canada Centre for Remote Sensing Tutorial: Fundamentals of Remote Sensing [http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca.earth-sciences/files/pdf/resource/tutor/fundam/pdf/fundamentals_e.pdf (PDF)]
 
−
#http://www.esa.int/SPECIALS/Eduspace_EN/SEMF9R3Z2OF_0.html
 
−
#http://eoedu.belspo.be/en/applications/index.htm
 
−
#http://earthobservatory.nasa.gov/Features/RemoteSensing/
 
−
#http://eoedu.belspo.be/en/applications/index.htm
 
−
#http://en.wikipedia.org/wiki/History_of_photography
 
−
#http://www.jpl.nasa.gov/jplhistory/early/firstsatellites.php
 
−
#http://www.geog.ucsb.edu/~jeff/115a/remotesensinghistory.html
 
−
</P>
 
−
{{Iseca}}
 
−
{{author
 
−
|AuthorID=26102
 
−
|AuthorFullName= Knockaert, Carolien
 
−
|AuthorName=Carolienk}}
 

Latest revision as of 16:12, 20 May 2024

Introduction

Fig. 1. Use of satellites as remote sensing platforms (Photo credit: ESA-AOES Medialab).

There is an increasing demand for accurate, timely information on natural resources and ecosystems, their spatial distribution and temporal changes and trends, from local to global. In the broadest sense, remote sensing is the measurement or acquisition of information about an object or phenomenon by a sensor that is not in direct physical contact with the object. Information is conveyed by waves radiating from the object. The sensor is mounted on a fixed frame (a mast) or on a moving platform, for example an aircraft, drone, satellite or a frame towed behind a ship.

Advantages of this technology are:

  • Observation of a large geographical area (from aircraft or satellite - Fig. 1)
  • Long-term and fast collection of data (from satellite)
  • Low collecting costs
  • "Inaccessible" regions become accessible (e.g. Antarctica)
  • Object is not being perturbed or destroyed

Disadvantages are:

  • Lower spatial resolution than in situ measurement (depending on the type of platform or sensor)
  • Initial investment in development and installation
  • Collected data need to be calibrated via in-situ data
  • Noise caused by another source than the desired one
  • Atmospheric effects degrade the quality of the images and need to be corrected


Brief history

1826 Invention of photography by Joseph Nicéphore Niépce
1850s Photography with cameras from hot-air balloons
1903 Invention of pigeon photography (used during World War I and the Civil War)
1904 Invention 'telemobiloscope', first radar-type device by Christian Hülsmeyer
1909 Photography from air planes
1913 First acoustic underwater transducer patented by Reginald A. Fessenden, precursor of the sonar (sound navigation and ranging).
World War I Military surveillance: airplanes with cameras
1920 First detailed seafloor maps using sonar by the US Coast and Geodetic Survey.
1922 Borehole radar using pulsed modulation patented by Loewy
1930 Invention of Lidar (acronym of "light detection and ranging" or "laser imaging, detection, and ranging") by E. H. Synge
1942 First ship radars for the fleets of the U.S. and British navy
1960s Space programs and race between the United States (US) and the Soviet-Union (USSR)
04 October 1957 Sputnik I (USSR): first artificial satellite to go into orbit
31 January 1958 Explorer I (US) is launched
1960 TIROS-1: first meteorological satellite. First use of term 'Remote sensing'
1961 First Lidar system developed by the Hughes Aircraft Company
1964 First application of marine X-band (or microwave) radar for ocean wave imaging by Ijima et al. (1964[1])
1972 Landsat-1: launch of the first earth resource satellite
1990s Launch of earth resource satellites by national space agencies and commercial companies



General principles of remote sensing

Remote sensors are devices that measure and record specific types of energy. This energy is electromagnetic radiation in remote sensing via the air; underwater remote sensing usually involves acoustic waves. The electromagnetic spectrum is the distribution of radiation energy over wavelengths. The spectrum can be divided into different spectral ranges: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves (Fig. 2). Remote sensing involves measuring energy in spectral bands - discrete intervals of the EM spectrum. Satellite sensors are designed to measure signals emitted by objects on the Earth's surface within certain spectral bands from which the characteristics of these objects can be inferred. Scientists choose a particular spectral band for data collection depending on what they want to investigate. The data recorded by the sensors must be pre-processed (corrected, enhanced), analyzed (classified) and interpreted to provide useful information. Simple traditional methods of visual interpretation have evolved into advanced mathematical and statistical methods using models and analysis techniques as described in Data analysis techniques for the coastal zone and many other articles in the Coastal Wiki.


Fig. 2. The electromagnetic spectrum (Photo credit: Johannes Ahlmann).


Types of sensors

Remote sensing systems can be divided into 2 categories: active and passive sensors. Active sensors (usually detection and ranging systems such as radar, sonar, Lidar) emit radiation which is directed toward the object or surface to be investigated. The radiation emitted by an active sensor provides a specific spectral energy pulse to the study object that activates a response signal which is detected, measured and timed by the sensor. It thus allows to determine distances (ranges). Passive systems (e.g. photographic camera) record the radiation emitted by an object that receives radiation (energy) from an external energy source (for example the sunlight). The radiation emitted by an object is due to reflection, backscatter (diffuse) and re-emitted back radiation. It can provide information about the shape (via reflected radiation), pattern, type of substance and composition of the object.


Fig. 3 The basic principle of ocean colour remote sensing: The radiance, which arrives at the satellite consists of 4 components: (1) radiance which is scattered in the atmosphere, (2) radiance which is specularly reflected at the sea surface, (3) radiance which is backscattered by water and its constituents and (4) in shallow water, radiance, which is reflected from the sea bottom. All 3, or in case of shallow water 4, components have to be determined to retrieve the radiance leaving the water, i.e. component 2.

Atmospheric effects

Remote sensors that observe the Earth are looking through the atmosphere. The atmospheric constituents (particles and gases) can affect the incoming light and radiation by causing wavelength-dependent absorption and scattering (Fig. 3). Scattering occurs when particles or large gas molecules present in the atmosphere interact with the electromagnetic radiation and cause it to be diverted from its original path. Absorption causes molecules in the atmosphere to absorb and re-emit energy at various wavelengths. Ozone, carbon dioxide and water vapor are the most important atmospheric constituents that absorb radiation. These atmospheric effects degrade the quality of the images. They need to be corrected for before the images are subjected to further analysis and interpretation. Sunglint, the direct reflection of the sun from the water surface to the sensor, is another effect that must be corrected for.

Remote sensing applications in the Coastal Wiki


Articles related to remote sensing

Satellite remote sensing

Light fields and optics in coastal waters
Optical remote sensing
Plankton remote sensing
Plankton remote sensing North Sea
Satellite-derived nearshore bathymetry
Oil spill monitoring
Use of Lidar for coastal habitat mapping
HyMap: Hyperspectral seafloor mapping and direct bathymetry calculation in littoral zones
Plankton remote sensing
Remote sensing of zooplankton
The Baltic Algae Watch System - a remote sensing application for monitoring cyanobacterial blooms in the Baltic Sea
Bathymetry from remote sensing wave propagation
Use of aerial photographs for shoreline position and mapping applications
SeaWiFS
MODIS
MERIS
Tidal flats from space
Detecting the unknown - novelty detection of exceptional water reflectance spectra
The HIMOM and OFEW approaches to monitoring intertidal flats

Radar remote sensing

Coastal ocean satellite altimetry
Waves and currents by X-band radar
Bathymetry German Bight from X-band radar
Measuring current fields in the German Bight by radar techniques
Application of radar hydrography in the German Wadden Sea
WiRAR - A marine radar wind sensor
WiSAR - Wind retrieval from synthetic aperture radar

Under water remote sensing

General principles of optical and acoustical instruments
Monitoring coastal morphodynamics using high-precision multibeam technology
Optical Laser diffraction instruments (LISST)
Remote sensing of zooplankton
Optical backscatter point sensor (OBS)
Instruments and sensors to measure environmental parameters
Acoustic monitoring of marine mammals
Acoustic point sensors (ASTM, UHCM, ADV)
Acoustic backscatter profiling sensors (ABS)
Currents and turbulence by acoustic methods
Acoustic kelp bed mapping in shallow rocky coasts - case study Helgoland (North Sea)
Instruments for bed level detection
Measuring instruments for fluid velocity, pressure and wave height

Video camera

Argus video monitoring system
Argus video
Underwater video systems
Video technology
Application and use of underwater video
Argus applications


The main authors of this article are Knockaert, Carolien and Job Dronkers
Please note that others may also have edited the contents of this article.
Citation: Knockaert, Carolien; Job Dronkers; (2024): Remote sensing. Available from http://www.coastalwiki.org/wiki/Remote_sensing [accessed on 22-11-2024]
  1. ↑ Ijima, T., Takahashi, T. and Sasaki, H. 1964. Application of radars to wave observations. Proc. 11th Int. Conf. Coastal Engineering 30: 10-22
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