The basis for multispectral collection and analysis is that of examined areas or objects that reflect or emit radiation that stand out from surrounding areas. For a summary of major remote sensing satellite systems see the overview table.
Applications of remote sensing taken by UmbraConventional radar is mostly associated with
air traffic control, early warning, and certain large-scale meteorological data.
Doppler radar is used by local law enforcements' monitoring of speed limits and in enhanced
meteorological collection such as wind speed and direction within weather systems in addition to precipitation location and intensity. Other types of active collection includes
plasmas in the
ionosphere.
Interferometric synthetic aperture radar is used to produce precise
digital elevation models of large scale terrain (See
RADARSAT,
TerraSAR-X,
Magellan). Laser and
radar altimeters on satellites have provided a wide range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so. By measuring the height and wavelength of ocean waves, the altimeters measure wind speeds and direction, and surface ocean currents and directions. Ultrasound (acoustic) and radar tide gauges are used to measure sea level, tides and wave direction in coastal and offshore tide gauges.
Light detection and ranging (LiDAR) is used for weapon ranging, laser illuminated homing of projectiles, and to detect and measure the concentration of various chemicals in the atmosphere while airborne LiDAR can be used to measure the heights of objects and features on the ground more accurately than radar technology. LiDAR can be used to detect ground surface changes typically by creating Digital Surface Models (DSMs) or Digital Elevation Models (DEMs). Vegetation remote sensing is a principal application of LIDAR. The most common instruments in use are
radiometers and
photometers, which collect reflected and emitted radiation in a wide range of frequencies. The most prevalent of these frequencies are visible and infrared sensors, followed by microwave, gamma-ray, and rarely, ultraviolet. They may also be used to detect the
emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere. Radiometers are also used at night, as
artificial light emissions are a key signature of human activity. Applications include remote sensing of population, GDP, and damage to infrastructure from war or disasters. Radiometers and radar onboard of satellites can be also used to monitor volcanic eruptions.
Spectropolarimetric Imaging has been reported to be useful for target tracking purposes by researchers at the
U.S. Army Research Laboratory. They determined that manmade items possess polarimetric signatures that are not found in natural objects. These conclusions were drawn from the imaging of military trucks, like the
Humvee, and trailers with their
acousto-optic tunable filter dual
hyperspectral and spectropolarimetric VNIR Spectropolarimetric Imager.
Stereographic pairs of
aerial photographs have often been used to make
topographic maps by imagery and terrain analysts in trafficability and highway departments for potential routes, in addition to modelling terrestrial habitat features. Simultaneous multi-spectral platforms such as Landsat have been in use since the early 1970s. These thematic mappers take images in multiple wavelengths and are usually found on
Earth observation satellites, including (for example) the
Landsat program or the
IKONOS satellite. Maps of
land cover and
land use from thematic mapping can be used to prospect for minerals, detect or monitor land usage, detect invasive vegetation, deforestation, and examine the health of indigenous plants and crops (
satellite crop monitoring), including entire farming regions or forests. Prominent scientists using remote sensing for this purpose include
Janet Franklin and
Ruth DeFries. Landsat images are used by regulatory agencies such as KYDOW to indicate water quality parameters including Secchi depth, chlorophyll density, and total phosphorus content.
Weather satellites are used in meteorology and climatology.
Hyperspectral imaging produces image cubes where each pixel has full spectral information with imaging narrow spectral bands over a contiguous spectral range. Hyperspectral imagers are used in various applications including mineralogy, biology, defence, and environmental measurements. Within the scope of the combat against
desertification, remote sensing allows researchers to follow up and monitor risk areas in the long term, to determine desertification factors, to support decision-makers in defining relevant measures of environmental management, and to assess their impacts. Remotely sensed multi- and hyperspectral images can be used for assessing biodiversity at different spatial scales. Since the spectral properties of different plants species are unique, it is possible to get information about properties that relates to biodiversity such as habitat heterogeneity, spectral diversity and plant functional trait. Remote sensing has also been used to detect rare plants to aid in conservation efforts. Prediction, detection, and the ability to record biophysical conditions were possible from medium to very high resolutions. Remote sensing is often utilized in the collection of agricultural and environmental statistics, usually combining classified satellite images with
ground truth data collected on a sample selected on an
area sampling frame Geodetic Geodetic remote sensing can be
gravimetric or geometric. Overhead gravity data collection was first used in aerial submarine detection. This data revealed minute perturbations in the Earth's
gravitational field that may be used to determine changes in the mass distribution of the Earth, which in turn may be used for geophysical studies, as in
GRACE. Geometric remote sensing includes position and deformation
imaging using
InSAR, LIDAR, etc.
Acoustic and near-acoustic Three main types of acoustic and near-acoustic remote sensing exist:
Sonar –
passive sonar, listening for the sound made by another object (a vessel, a whale etc.);
active sonar, emitting pulses of sounds and listening for echoes, used for detecting, ranging and measurements of underwater objects and terrain.
Seismograms taken at different locations can locate and measure
earthquakes (after they occur) by comparing the relative intensity and precise timings.
Ultrasound acoustic sensing is made up of ultrasound sensors that emit high-frequency pulses and listening for echoes, used for detecting water waves and water level, as in tide gauges or for towing tanks. To coordinate a series of large-scale observations, most sensing systems depend on the following: platform location and the orientation of the sensor. High-end instruments now often use positional information from
satellite navigation systems. The rotation and orientation are often provided within a degree or two with electronic compasses. Compasses can measure not just azimuth (i. e. degrees to magnetic north), but also altitude (degrees above the horizon), since the magnetic field curves into the Earth at different angles at different latitudes. More exact orientations require
gyroscopic-aided orientation, periodically realigned by different methods including navigation from stars or known benchmarks.
Gamma rays There are applications of
gamma rays to mineral exploration through remote sensing. In 1972 more than $2 million were spent on remote sensing applications with gamma rays to mineral exploration. Gamma rays are used to search for deposits of
uranium. By observing radioactivity from potassium,
porphyry copper deposits can be located. A high ratio of uranium to thorium has been found to be related to the presence of hydrothermal copper deposits. Radiation patterns have also been known to occur above oil and gas fields, but some of these patterns were thought to be due to surface soils instead of oil and gas. == Data characteristics ==