**4.1. Optical imaging sensors**

wavelength of 310 nm, the reflectance of aluminum is zero [25]. The reflectance of gold significantly increases at a wavelength of approximately 500 nm, reaching a very high reflectance starting in the infrared. This figure indicates that regardless of the wavelength at which the

The physical characteristics of the material determine what type of electromagnetic waves will and will not pass through it. **Figure 5** shows examples of the reflection spectrums of dry bare soil, green vegetation, and clear water. The reflection of dry bare soil increase as the wavelength increases from 400 to 1800 nm. Green vegetation has a high reflectance in the red light and near-infrared regions. These characteristics have been applied for distinguishing green vegetation from other objects. In addition, the previous figure shows that water has a low absorbance in the visible light region. **Figure 5** shows that water reflects visible light at a low rate (<5%). Indirectly, the figure indicates that water has a high transmittance in the vis-

sensor operates, it is inevitable to encounter high reflection from aluminum surfaces.

**Figure 4.** Reflective spectrum of metals: aluminum, gold, and silver.

28 Multi-purposeful Application of Geospatial Data

**Figure 5.** Examples of reflective materials. Image referenced from Wikimedia [26].

ible light range.

Optical imaging sensors operate in the visible and reflective IR ranges. Typical optical imaging systems on space platform include panchromatic systems, multispectral systems, and hyperspectral systems. In a panchromatic system, the sensor is a monospectral channel detector that is sensitive to radiation within a broad wavelength range. The image is black and white or gray scale. A multispectral sensor is a multichannel detector with a few spectral bands. Each channel is sensitive to radiation within a narrow wavelength band. The resulting image is a multilayer image that contains both the brightness and spectral (color) information of the targets being observed. A hyperspectral sensor collects and processes information from 10 to 100 of spectral bands. A hyperspectral image consists of a set of images. Each narrow spectral band forms an image. The resulting images can be utilized to recognize objects, identify materials, and detect elemental components. **Table 2** gives a more detailed description of

**Figure 6.** Spaceborne remote sensing sensors.


**4.3. Radar imaging sensors**

**Table 3.** Thermal IR sensors.

**Sensor Operational** 

IR imaging radiometer

Imaging spectroradiometer

Infrared imaging camera

**wave band**

UV, mid-tofar-infrared, or microwave

image with a half meter of accuracy [32].

A radar (microwave) imaging sensor is usually an active sensor, operating in an electromagnetic spectrum range of 1 mm–1 m. The sensor transmits light to the ground, and the energy is reflected from the target to the radar antenna to produce an image at microwave wavelengths. The radar moves along a flight path, and the area illuminated by the radar, or footprint, is moved along the surface in a swath. Each pixel in the radar image represents the radar backscatter for that area on the ground. A microwave instrument can operate in cloudy or foggy weather and can also penetrate sand, water, and walls. Unlike infrared data that help us identify different minerals and vegetation types from reflected sunlight, radar only shows the difference in the surface roughness and geometry and the moisture content of the ground (the complex dielectric constant). Radar and infrared sensors are complimentary instruments and are often used together to study the same types of Earth surfaces [30]. Frequently used microwave spectrum bands for remote sensing include the X-band, C-band, S-band, L-band,

**Definition Satellites** 

Measures the intensity of electromagnetic radiation

of radiation in multiple

energy from the surface

Infrared Measure the intensity

Mid-far infrared Measure reflected

spectrums

**sensors**

MODIS, ASAS, IRIS

**Applications**

ASTER Volcanological, mineralogical,

the atmosphere

fog and low clouds

and hydrothermal studies, forest fires, glacier, limnological and climatological studies and DEM

http://dx.doi.org/10.5772/intechopen.71049

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Sea surface temperature, cloud characteristics, ocean color, vegetation, trace chemical species in

Volcanology, determining thunderstorm intensity, identifying

Conventional passive microwave imaging instruments (such as cameras or imaging radiometers) provide imagery with a relatively coarse spatial resolution when compared to an optical instrument. The diffraction-limited angular resolution of a camera aperture is directly proportional to the wavelength and inversely proportional to the aperture dimension [33]. To achieve a similar spatial resolution as optical instruments, a large antenna aperture (e.g., tens of kilometers) is needed. Clearly, it is not feasible to carry such a large antenna on a space platform. SAR is an active microwave instrument that resolves the above problem. SAR utilizes the motion of the spacecraft to emulate a large antenna from the small craft itself. The longer the antenna is, the narrower the beam is. A fine ground resolution usually results from a narrow beam width. At present, a synthesized aperture can be several orders of magnitude larger than the transmitter and receiver antenna. It has become possible to produce an SAR

and P-band. Specific characteristics of each band can be found in **Table 4**.

**Table 2.** Satellite optical imaging systems.

these optical imaging systems. It can be seen that when a light is split into multiple spectrums, the greater the number of spectrums is, the lower the imaging resolution will be. That is, a panchromatic image usually presents a higher resolution than a multispectral/hyperspectral image. Pan-sharpening technique was introduced by Padwick et al. in 2010 [29] for improving the quality of multispectral images. This method combines the visual information of the multispectral data with the spatial information of the panchromatic data, resulting in a higher resolution color product equal to the panchromatic resolution.

#### **4.2. Thermal IR imaging sensors**

A thermal sensor typically operates in the electromagnetic spectrum between the midto-far-infrared and microwave ranges, roughly between 9 and 14 μm. Any object with a temperature above zero can emit infrared radiation and produce a thermal image. A warm object emits more thermal energy than a cooler object. Therefore, the object becomes more visible in an image. This is especially useful in tracking a living creature, including animals and the human body, and detecting volcanos and forest fires because a thermal image is independent from the lights in a scene and is available whether it is daytime or nighttime. Commonly used thermal imaging sensors include IR imaging radiometers, imaging spectroradiometers, and IR imaging cameras. Currently, the satellite IR sensors in use include ASTER, MODIS, ASAA, and IRIS. **Table 3** lists the thermal IR sensors and their applications.


**Table 3.** Thermal IR sensors.

these optical imaging systems. It can be seen that when a light is split into multiple spectrums, the greater the number of spectrums is, the lower the imaging resolution will be. That is, a panchromatic image usually presents a higher resolution than a multispectral/hyperspectral image. Pan-sharpening technique was introduced by Padwick et al. in 2010 [29] for improving the quality of multispectral images. This method combines the visual information of the multispectral data with the spatial information of the panchromatic data, resulting in a higher

fires, all in a single image

Advantages High applicability in (i) imaging multiple targets; (ii) mosaic strips to large area; (iii) stereo and

Disadvantages Affected by sun illumination and cloud coverage. Polar areas with seasonal changes in sun illumination and the equatorial belt with persistent cloud coverage

**Panchromatic systems Multispectral systems Hyperspectral systems**

Red-green-blue (true color): visual analysis; Green-red-infrared: vegetation and camouflage detection; Blue-NIR-MIR: visualizing water depth, vegetation coverage, soil moisture content, and the presence of

tristereo acquisition; (iv) linear feature acquisition, such as coastlines, pipelines, roads, and borders

~470–2000

(i) Agriculture; (ii) eye care; (iii) food processing; (iv) mineralogy; (v) surveillance; (vi) physics; (vii) astronomy; (viii) chemical imaging; (ix)

environment

Several spectral bands 10 to 100 of spectral bands

~750–950

Satellites QuickBird, SPOT, IKONOS SPOT, QuickBird, IKONOS TRW Lewis, EO-1

Submeter Up to 1–2 m Up to 2 m

A thermal sensor typically operates in the electromagnetic spectrum between the midto-far-infrared and microwave ranges, roughly between 9 and 14 μm. Any object with a temperature above zero can emit infrared radiation and produce a thermal image. A warm object emits more thermal energy than a cooler object. Therefore, the object becomes more visible in an image. This is especially useful in tracking a living creature, including animals and the human body, and detecting volcanos and forest fires because a thermal image is independent from the lights in a scene and is available whether it is daytime or nighttime. Commonly used thermal imaging sensors include IR imaging radiometers, imaging spectroradiometers, and IR imaging cameras. Currently, the satellite IR sensors in use include ASTER, MODIS, ASAA, and IRIS. **Table 3** lists the thermal IR sensors and their

resolution color product equal to the panchromatic resolution.

~430–720 ~430–720

**4.2. Thermal IR imaging sensors**

**Table 2.** Satellite optical imaging systems.

applications.

Spectral range (nm)

Spatial resolution

Spectral band Monospectral, black and

30 Multi-purposeful Application of Geospatial Data

Applications Earth observation and

white, gray-scale image

reconnaissance applications

#### **4.3. Radar imaging sensors**

A radar (microwave) imaging sensor is usually an active sensor, operating in an electromagnetic spectrum range of 1 mm–1 m. The sensor transmits light to the ground, and the energy is reflected from the target to the radar antenna to produce an image at microwave wavelengths. The radar moves along a flight path, and the area illuminated by the radar, or footprint, is moved along the surface in a swath. Each pixel in the radar image represents the radar backscatter for that area on the ground. A microwave instrument can operate in cloudy or foggy weather and can also penetrate sand, water, and walls. Unlike infrared data that help us identify different minerals and vegetation types from reflected sunlight, radar only shows the difference in the surface roughness and geometry and the moisture content of the ground (the complex dielectric constant). Radar and infrared sensors are complimentary instruments and are often used together to study the same types of Earth surfaces [30]. Frequently used microwave spectrum bands for remote sensing include the X-band, C-band, S-band, L-band, and P-band. Specific characteristics of each band can be found in **Table 4**.

Conventional passive microwave imaging instruments (such as cameras or imaging radiometers) provide imagery with a relatively coarse spatial resolution when compared to an optical instrument. The diffraction-limited angular resolution of a camera aperture is directly proportional to the wavelength and inversely proportional to the aperture dimension [33]. To achieve a similar spatial resolution as optical instruments, a large antenna aperture (e.g., tens of kilometers) is needed. Clearly, it is not feasible to carry such a large antenna on a space platform. SAR is an active microwave instrument that resolves the above problem. SAR utilizes the motion of the spacecraft to emulate a large antenna from the small craft itself. The longer the antenna is, the narrower the beam is. A fine ground resolution usually results from a narrow beam width. At present, a synthesized aperture can be several orders of magnitude larger than the transmitter and receiver antenna. It has become possible to produce an SAR image with a half meter of accuracy [32].


amount of water content, it will be fairly absorptive to terahertz light. Therefore, this radiation can be applied in detecting lake shores or coastlines. InSAR, also called interferometric SAR, is a technique that produces measurements from two or more SAR images. This technique is widely applied in DEM production and monitoring glaciers, earthquakes, and volcanic eruptions [34]. D-InSAR requires taking at least two images with the addition of a DEM. The DEM can be acquired from GPS measurements. This method is mainly used for monitoring subsidence movements, slope stability analysis, landslides, glacier movement, and 3D ground movement [35]. Doppler radar is used to acquire a distant object's velocity relative to the radar. The main applications of this technique include aviation, sounding satellites, and meteorology. In

**Definition Application**

Calculating various surface and atmospheric parameters

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Mapping ocean-surface topography and the hills and valleys of the sea

Multispectral and hyperspectral

Monitoring sea surface temperature, cloud characteristics, ocean color, vegetation, trace chemical species in

Meteorology, cloud measurements, wind profiling and air quality

Meteorology: atmospheric research, wind monitoring (typically in a range from 50 to 200 m above ground level)

Is added to a radar wind profiler or

to a sodar system

Navigation, communication and security (e.g., vessels) and underwater object detection. For example, handheld sonar for a diver

surface

imaging

mapping

monitoring

To measure distance and intensity Ocean, land, 3D topographic

the atmosphere

To measure the amount of electromagnetic

To measure the altitude of an object above

To measure the spectral content of the incident electromagnetic radiation

To measure the intensity of radiation in

Doppler LIDAR: measure the wave number for speed; Polarization effects of

determine the depth of water beneath

wind speeds at various heights above the ground and the thermodynamic structure of the lower layer of the atmosphere

Measuring the atmospheric lapse rate using backscattering of radio waves from an acoustic wave front to measure the speed of sound at various heights above

energy present within a specific

general, SAR can reach a spatial resolution on the order of a millimeter.

wavelength range

multiple spectrums

LIDAR: shape

ships and boats

Sodar Acoustic As a wind profiler, sodar systems measure

the ground

Sonar Acoustic Measure the distance to an object;

a fixed level

**Sensor Operational** 

Radiometer Ultraviolet, IR, microwave

Spectrometer Visible, IR,

LIDAR Ultraviolet,

A radio acoustic sounding system (RASS)

**Table 5.** Non-imaging sensors.

Altimeter IR,

Spectroradiometer **wave band**

microwave/ radiowave, sonic

microwave

Visible, IR, microwave

visible, NIR

Radio wave and acoustic wave

**Table 4.** Commonly used frequency and spectrum bands of radar imaging sensors.

Specifically, SAR uses microwaves to illuminate a ground target with a side-looking geometry and measures the backscatter and traveling time of the transmitted waves reflected by objects on the ground. The distance the SAR device travels over a target in the time taken for the radar pulses to return to the antenna produces the SAR image. Typically, SAR is mounted on a moving platform, such as a spaceborne or airborne platform. According to the combination of frequency bands and polarization modes used in data acquisition, SAR can be categorized into [33]:


The main parameters of designing and operating SAR include the power of electromagnetic energy, frequency, phase, polarization, incident angle, spatial resolution, and swath width. There are different types of SAR techniques, including ultra-wideband SAR, terahertz SAR, differential interferometry (D-InSAR), and interferometric SAR (InSAR). Ultra-wideband SAR utilizes a very wide range of frequencies of radio waves. This method results in a better resolution and more spectral information on target reflectivity. Therefore, this approach can be applied for scanning a smaller object or a closer area. Terahertz radiation works in the spectral range from 0.3 to 10 THz, typically between infrared and microwave. Typical characteristics of this wavelength range include its transmission through plastics, ceramics, and even papers. Terahertz radiation is extraordinarily sensitive to water content. If the material has even a small amount of water content, it will be fairly absorptive to terahertz light. Therefore, this radiation can be applied in detecting lake shores or coastlines. InSAR, also called interferometric SAR, is a technique that produces measurements from two or more SAR images. This technique is widely applied in DEM production and monitoring glaciers, earthquakes, and volcanic eruptions [34]. D-InSAR requires taking at least two images with the addition of a DEM. The DEM can be acquired from GPS measurements. This method is mainly used for monitoring subsidence movements, slope stability analysis, landslides, glacier movement, and 3D ground movement [35]. Doppler radar is used to acquire a distant object's velocity relative to the radar. The main applications of this technique include aviation, sounding satellites, and meteorology. In general, SAR can reach a spatial resolution on the order of a millimeter.


**Table 5.** Non-imaging sensors.

Specifically, SAR uses microwaves to illuminate a ground target with a side-looking geometry and measures the backscatter and traveling time of the transmitted waves reflected by objects on the ground. The distance the SAR device travels over a target in the time taken for the radar pulses to return to the antenna produces the SAR image. Typically, SAR is mounted on a moving platform, such as a spaceborne or airborne platform. According to the combination of frequency bands and polarization modes used in data acquisition, SAR can be categorized

The main parameters of designing and operating SAR include the power of electromagnetic energy, frequency, phase, polarization, incident angle, spatial resolution, and swath width. There are different types of SAR techniques, including ultra-wideband SAR, terahertz SAR, differential interferometry (D-InSAR), and interferometric SAR (InSAR). Ultra-wideband SAR utilizes a very wide range of frequencies of radio waves. This method results in a better resolution and more spectral information on target reflectivity. Therefore, this approach can be applied for scanning a smaller object or a closer area. Terahertz radiation works in the spectral range from 0.3 to 10 THz, typically between infrared and microwave. Typical characteristics of this wavelength range include its transmission through plastics, ceramics, and even papers. Terahertz radiation is extraordinarily sensitive to water content. If the material has even a small

into [33]:

**Band Frequency (GHz)**

**Wavelength (cm)**

32 Multi-purposeful Application of Geospatial Data

Ka 40–27 0.75–1.11 Usually for astronomical observations

Ku 18–12 1.67–2.5 Typically used for satellite communications

**Table 4.** Commonly used frequency and spectrum bands of radar imaging sensors.

**Key characteristics**

automotive radar

K 27–18 1.11–1.67 Used for radar, satellite communications, astronomical observations,

X 12.5–8 2.4–3.75 Widely used for military reconnaissance, mapping and surveillance

C 4–8 3.75–7.5 Penetration capability of vegetation or solids is limited and restricted to the top layers. Useful for sea-ice surveillance S 4–2 7.5–15 Used for medium-range meteorological applications, for example, rainfall measurement, airport surveillance L 2–1 15–30 Penetrates vegetation to support observation applications over vegetated

P 1–0.3 30–100 So far, only for research and experimental applications. Significant penetration

surfaces and for monitoring ice sheet and glacier dynamics

capabilities regarding vegetation canopy, sea ice, soil, and glaciers

• Single frequency (L-band, C-band, or X-band);

• Single polarization (VV, HH, or HV);

Referenced from Born and Wolf [31].

• Multiple frequency (Combination of two or more frequency bands);

• Multiple polarization (Combination of two or more polarization modes).

#### **4.4. Non-imaging sensors**

A non-imaging sensor measures a signal based on the intensity of the whole field of view, mainly as a profile recorder. In contrast with imaging sensors, this type of sensor does not record how the input varies across the field of view. In the remote sensing field, the commonly used non-imaging sensors include radiometers, altimeters, spectrometers, spectroradiometers, and LIDAR. **Table 5** provides detailed information about conventional non-imaging sensors. In the remote sensing field, non-imaging sensors typically work in the visible, IR, and microwave spectral bands. The applications for non-imaging sensors mainly focus on height, temperature, wind speed, and other atmospheric parameter measurements.

Lasers have been applied in measuring the distance and height of targets in the remote sensing field. We generally call a laser scanning system as LIDAR (light detection and ranging) system. Satellite LIDAR, airborne LIDAR, mobile mapping LIDAR, and terrestrial LIDAR are different carrier platforms. Laser sources include solid-state lasers, liquid lasers, gas lasers, semiconductor lasers, and chemical lasers (see **Table 6**). Typical laser sources for laser rangefinders and laser altimeters include semiconductor laser and solid-state lasers. Semiconductor lasers typically produce light sources at wavelengths of 400–500 nm and 850–1500 nm. Solidstate lasers generate light at wavelengths of 700–820 nm, 1064 nm, and 2000 nm. Satellite or airborne LIDAR systems are typically operated at wavelengths of 905 , 1064 and 1550 nm. One of the main considerations for wavelength selection is the atmospheric transmission between the sensor and the surface of the Earth. Lower transmittance at a given wavelength means less solar radiation at that wavelength. The transmittance at 905 nm is approximately 0.6, while the wavelengths of 1064 and 1550 nm have similar transmittances of approximately 0.85. In addition, wavelength selection can also be a cost issue. Diode lasers at 905 nm are inexpensive compared to Nd:YAG solid-state lasers at 1064 nm and diode lasers at 1550 nm. In 2007, the cost of diode lasers at 1550 nm was 2.5 times higher than lasers at 905 nm. However, the wavelength

of 1550 nm is a good candidate for use in invisible wavelength eye-safe LIDAR. The higher absorption of 1550 nm light by water makes it eye safe, and this absorption is approximately 175 times greater than that of 905 nm light. In addition, the solar background level of light at 1550 nm is approximately 50% lower than that of light at 905 nm. Making measurements at 1550 nm also results in a higher signal to noise ratio compared to using a beam at 905 nm. All in all, when ignoring the cost issue, a wavelength of 1550 nm has a clear advantage over light

Airborne laser scanning

Airborne laser scanning

**Laser sources Typical applications**

Blue laser 488 Solid-state laser Environmental monitoring, medical diagnostics,

Laser printing, data recording, laser microscopy, laser projection displays, spectroscopic measurements

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handheld projectors and displays, telecommunications

UV laser 355 Gas laser Cutting and drilling

Green laser 532 Solid-state laser (Nd:YAG) Bathymetric measurement Red laser 640 Semiconductor laser Vegetation measurement

solid-state laser (fiber laser)

solid-state laser (fiber laser)

solid-state laser

Violet laser 405 Semiconductor laser or

NIR laser 1064 Semiconductor laser or

NIR laser 1550 Semiconductor laser or

**Table 7.** Commonly used laser wavelength.

In general, at a wavelength of 1064 nm, vegetation has stronger reflectance than soil, while at a wavelength of 1550 nm, soil shows greater a reflectance than vegetation. Taking measurements with different wavelengths is beneficial for object classification. Green lasers with a wavelength of 532 nm are usually pumped by a solid-state laser (Nd:YAG). This type of laser is widely used for bathymetric measurement. **Table 7** lists the typical applications of different

So far, more than 1000 remote sensing satellites have been launched. These satellites have been updated with new generation satellites. The few spectral sensors from the earliest missions have been upgraded to hyperspectral sensors with hundreds of spectral bands. The spatial and spectral resolutions have been improved on the order of 100-fold. Revisit times have been shortened from months to daily. In addition, more and more remote sensing data are available as open data sources. **Table 8** gives an overview of the commonly used remote

at 905 nm [36].

Referenced from Hey [36].

**Name wavelength (nm)**

laser light wavelengths.

**4.5. Commonly used remote sensing satellites**

sensing satellites and their parameters.


**Table 6.** Typical laser sources.


**Table 7.** Commonly used laser wavelength.

**4.4. Non-imaging sensors**

34 Multi-purposeful Application of Geospatial Data

measurements.

A non-imaging sensor measures a signal based on the intensity of the whole field of view, mainly as a profile recorder. In contrast with imaging sensors, this type of sensor does not record how the input varies across the field of view. In the remote sensing field, the commonly used non-imaging sensors include radiometers, altimeters, spectrometers, spectroradiometers, and LIDAR. **Table 5** provides detailed information about conventional non-imaging sensors. In the remote sensing field, non-imaging sensors typically work in the visible, IR, and microwave spectral bands. The applications for non-imaging sensors mainly focus on height, temperature, wind speed, and other atmospheric parameter

Lasers have been applied in measuring the distance and height of targets in the remote sensing field. We generally call a laser scanning system as LIDAR (light detection and ranging) system. Satellite LIDAR, airborne LIDAR, mobile mapping LIDAR, and terrestrial LIDAR are different carrier platforms. Laser sources include solid-state lasers, liquid lasers, gas lasers, semiconductor lasers, and chemical lasers (see **Table 6**). Typical laser sources for laser rangefinders and laser altimeters include semiconductor laser and solid-state lasers. Semiconductor lasers typically produce light sources at wavelengths of 400–500 nm and 850–1500 nm. Solidstate lasers generate light at wavelengths of 700–820 nm, 1064 nm, and 2000 nm. Satellite or airborne LIDAR systems are typically operated at wavelengths of 905 , 1064 and 1550 nm. One of the main considerations for wavelength selection is the atmospheric transmission between the sensor and the surface of the Earth. Lower transmittance at a given wavelength means less solar radiation at that wavelength. The transmittance at 905 nm is approximately 0.6, while the wavelengths of 1064 and 1550 nm have similar transmittances of approximately 0.85. In addition, wavelength selection can also be a cost issue. Diode lasers at 905 nm are inexpensive compared to Nd:YAG solid-state lasers at 1064 nm and diode lasers at 1550 nm. In 2007, the cost of diode lasers at 1550 nm was 2.5 times higher than lasers at 905 nm. However, the wavelength

Gas laser Electrical discharge Interferometry, holography, spectroscopy, material processing

Metal-vapor laser Electrical discharge Printing and typesetting applications, fluorescence excitation

examination, scientific research

Electrical current Telecommunications, holography, printing, weapons, machining

Material processing, rangefinding, laser target designation

**Laser types Pump source Typical applications**

Dye laser Other laser, flashlamp Research, laser medicine

Chemical laser Chemical reaction Military use

Solid-state laser Flashlamp, laser diode, Fiber laser, Nd: YAG.

Semiconductor

**Table 6.** Typical laser sources.

laser

of 1550 nm is a good candidate for use in invisible wavelength eye-safe LIDAR. The higher absorption of 1550 nm light by water makes it eye safe, and this absorption is approximately 175 times greater than that of 905 nm light. In addition, the solar background level of light at 1550 nm is approximately 50% lower than that of light at 905 nm. Making measurements at 1550 nm also results in a higher signal to noise ratio compared to using a beam at 905 nm. All in all, when ignoring the cost issue, a wavelength of 1550 nm has a clear advantage over light at 905 nm [36].

In general, at a wavelength of 1064 nm, vegetation has stronger reflectance than soil, while at a wavelength of 1550 nm, soil shows greater a reflectance than vegetation. Taking measurements with different wavelengths is beneficial for object classification. Green lasers with a wavelength of 532 nm are usually pumped by a solid-state laser (Nd:YAG). This type of laser is widely used for bathymetric measurement. **Table 7** lists the typical applications of different laser light wavelengths.

#### **4.5. Commonly used remote sensing satellites**

So far, more than 1000 remote sensing satellites have been launched. These satellites have been updated with new generation satellites. The few spectral sensors from the earliest missions have been upgraded to hyperspectral sensors with hundreds of spectral bands. The spatial and spectral resolutions have been improved on the order of 100-fold. Revisit times have been shortened from months to daily. In addition, more and more remote sensing data are available as open data sources. **Table 8** gives an overview of the commonly used remote sensing satellites and their parameters.


**Mission** WorldView

USA

2007

Imaging spectroradiometer,

496,

17.6 km

1.7

Panchromatic;

Panchromatic 0.5

 m; Panchromatic and stereo

images:0.46 m

multispectral: 1.84

Panchromatic 0.34

multispectral 1.36

 m

 m and

 m;

Panchromatic and eight

1.1

<1

multispectrum;

Panchromatic and eight

multispectrum;

Panchromatic, B, G, R,

NIR

770,

16.4 km

617,

13.1 km

681

14.5 km

3

Laser altimeter

2009

2014

2016.9

Sentinel

ESA

2014, 2015,

Radar and super-spectral

693,

250 km

12, 10,

C-SAR, 12 bands (VIS,

5–20 m, 5–40 m, 10 m & 20 m & 60 m

NIR, SWIR), 21 bands

(VIS, NIR), S-band &

X-band

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786,

290 km,

27

814

250 km,

2016,

imaging

2017, 2021

Referenced from Refs. [37–40].

**Table 8.**

Remote sensing satellites.

1–6

**Country**

**Launch year**

**Sensors**

**Height** 

**Swath (km)**

**Revisit** 

**Channels**

**Spatial resolution**

**(day)**

**of orbit** 

**(km)**


**Mission** Landsat

USA

1972, 1975,

Panchromatic and

multispectral sensor

1978,1982,

1984,1993,

1999,2013, 2020

SPOT

ERS RADARSAT

MODIS IKONOS QuickBird

Envisat GeoEye

USA

2008

ESA

2002

ASAR, MERIS, AATSR, RA-2,

790

1150 km,

35 days

15 bands (VIS, NIR),

300

m, 30–150 m

C-band

100 km,

400 km

MWR, GOMOS, MIPAS,

SCIAMACHY, DORIS, LRR

Imaging spectroradiometer

681

15.2

8.3

Panchromatic, B, G, R,

Panchromatic:41

B, G, R, NIR: 1.65

 m

 cm

NIR

USA

2000, 2001

Imaging spectroradiometer

482,

16.8–18

2.4–5.9

Panchromatic, B, G, R,

NIR

450

USA

1999

USA

1999, 2002

Imaging spectroradiometer

Imaging spectroradiometer

681

11.3

3

Panchromatic, B, G, R,

Panchromatic:80

B, G, R, NIR:3.2

Panchromatic:65

B, G, R, NIR:2.62

 m/2.44 m

 cm/61 cm

 m

 cm

NIR

705

2330

1

36

1000 m, 500 m, 250 m

Canada

1995, 2007, 2018

SAR

793–

45–100,

1

SAR

8–100 3–100 m

m, 3–100 m,

821,

18–500,

798,

5–500

592.7

ESA

1991, 1995

IR radiometer, microwave

782–785

5–100 km

3, 35,

SAR

26 6–30

m along track

m across track and

(AMI) -

336

500 km

(ATSR)

sounder, Radiometer, SAR

USA

1986, 1990, 1993,

Imaging spectroradiometer

694

60

1–3

Panchromatic, B, G, R,

2.5 m, 5 m, 10 m, 20 m

36 Multi-purposeful Application of Geospatial Data

NIR

1998, 2002, 2012

**Country**

**Launch year**

**Sensors**

**Height** 

**Swath (km)**

**Revisit** 

**Channels**

**Spatial resolution**

**(day)**

**of orbit** 

**(km)**

705

185, 183

16

7–11

120 m, 100 m, 60 m, 30 m,

15 m

> **Table 8.** Remote sensing satellites.
