First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment

Generic-Gamma Ray Sensors (Gen-Gamma) refer to non-specific instruments on a platform used to measure gamma-ray radiation. They are typically passive sensors that detect the energy of emitted gamma radiation. Gamma-ray measurements are used to identify radioactive isotopes for environmental monitoring and geological studies.

Radiosondes are a balloon-borne instrument package used to collect profile measurements of pressure, temperature, humidity, and winds. These sensors are connected to a radio transmitter that sends the measurements to a ground receiver typically operating in the 400-406 MHz range. They typically provide measurements at 1-6 seconds, depending on the type and manufacturer of the radiosonde. Radiosondes are used for weather forecasting, ground truth satellite data, atmospheric research, and input for weather prediction models.

The Side-Looking Airborne Radar (SLAR) is an airborne imaging system that points perpendicular to the flight direction. SLAR sends a beam of energy to the surface perpendicular to the flight path and detects the return signals to create radar images of the terrain. It usually operates in the X-band (8-12 GHz). SLAR can gather imagery regardless of weather or time of day and has been used for mapping geological features and cloud-covered regions because of its ability to penetrate clouds.

The Lyman-alpha Hygrometer is an in situ hygrometer designed for deployment on airborne or ground-based platforms. It measures water vapor absorption at the Lyman-alpha wavelength (121.6 nm) of atomic hydrogen to determine the total water content in the atmosphere. It has a detection limit of 0.1 ppmv and a typical data acquisition rate of 1 second. The Lyman-alpha hygrometer provides water vapor measurements with an accuracy of 6% and a precision of 5%.

Generic-Atmospheric State (Gen-AtmsState) refers to non-specific instruments on a platform used for measurements of atmospheric state parameters. These are typically in situ sensors that measure temperature, pressure, humidity, and wind speed/direction. Types of atmospheric state instruments include thermometers, hygrometers, barometers, and anemometers.

Rosemount Pressure Probes are in situ airborne pressure sensors manufactured by Rosemount, Inc. They provide high-precision atmospheric pressure measurements and are typically used to gather flight-level meteorological observations. Rosemount Pressure Probes consist of various pressure transducers, gauges, and multivariable and coplanar transmitters.

Rosemount Temperature Probes are in situ airborne temperature sensors manufactured by Rosemount, Inc. They provide atmospheric temperature measurements and are typically used to collect flight-level meteorological observations. Rosemount Temperature Probes consist of temperature transmitters, thermocouple sensors, resistance temperature detectors, and other temperature sensors.

Generic-Atmospheric State (Gen-AtmsState) refers to non-specific instruments on a platform used for measurements of atmospheric state parameters. These are typically in situ sensors that measure temperature, pressure, humidity, and wind speed/direction. Types of atmospheric state instruments include thermometers, hygrometers, barometers, and anemometers.

Rosemount Pressure Probes are in situ airborne pressure sensors manufactured by Rosemount, Inc. They provide high-precision atmospheric pressure measurements and are typically used to gather flight-level meteorological observations. Rosemount Pressure Probes consist of various pressure transducers, gauges, and multivariable and coplanar transmitters.

Accelerometers are in situ sensors that measure the acceleration experienced by an object. Accelerometers utilize electromagnetic sensing to detect the vibration of an object. The force of vibration causes the sensor to produce an electrical charge, indicating how much force was exerted, which can be used to determine the acceleration. Accelerometers are typically used on aircraft when collecting flight navigation information. Accelerometers have also been deployed on research vessels and other water-based platforms such as buoys.

The Precision Radiation Thermometer (PRT-5) is an in situ infrared temperature sensor. It makes non-contact infrared (8-14 μm) temperature measurements between -50 to 150 degrees Celsius with an accuracy of 0.5 degrees Celsius. It has a typical field of view of 2 degrees and a response time of either 0.3 Hz, 3 Hz, or 30 Hz. PRT-5 can be deployed on aircraft, vehicles, research vessels, and other ground-based platforms. It can be used for sea surface, ocean water, cloud, and air temperature measurements.

Rosemount Temperature Probes are in situ airborne temperature sensors manufactured by Rosemount, Inc. They provide atmospheric temperature measurements and are typically used to collect flight-level meteorological observations. Rosemount Temperature Probes consist of temperature transmitters, thermocouple sensors, resistance temperature detectors, and other temperature sensors.

Video cameras capture video recordings of various phenomena for research purposes. They are used on aircraft to provide continuous views of weather and terrain below the flight path. Video cameras are also employed to verify the aircraft's flight track. Additionally, they are deployed at field sites to monitor changes in vegetation, land cover, clouds, air quality, glaciers, and other Earth science phenomena.

A pyranometer is a ground-based or airborne radiation sensor that measures solar irradiance across a hemispherical field of view. It detects the amount of solar energy reaching the surface, capturing both direct and diffuse sunlight. Pyranometers operate within a spectral range of 280-3000 nm. They are most commonly used for solar monitoring, climate research, weather forecasting, agriculture, and energy management.

The Side-Looking Airborne Radar (SLAR) is an airborne imaging system that points perpendicular to the flight direction. SLAR sends a beam of energy to the surface perpendicular to the flight path and detects the return signals to create radar images of the terrain. It usually operates in the X-band (8-12 GHz). SLAR can gather imagery regardless of weather or time of day and has been used for mapping geological features and cloud-covered regions because of its ability to penetrate clouds.

Generic-Atmospheric State (Gen-AtmsState) refers to non-specific instruments on a platform used for measurements of atmospheric state parameters. These are typically in situ sensors that measure temperature, pressure, humidity, and wind speed/direction. Types of atmospheric state instruments include thermometers, hygrometers, barometers, and anemometers.

Rosemount Pressure Probes are in situ airborne pressure sensors manufactured by Rosemount, Inc. They provide high-precision atmospheric pressure measurements and are typically used to gather flight-level meteorological observations. Rosemount Pressure Probes consist of various pressure transducers, gauges, and multivariable and coplanar transmitters.

The King Probe is an in situ airborne cloud instrument developed by Warren King (Commonwealth Scientific and Industrial Research Organisation) and manufactured by Particle Measuring Systems (PMS) and Droplet Measurement Technologies (DMT). The King Probe measures cloud liquid water content (LWC) by detecting the heat released when water droplets vaporize. It operates at a constant temperature of approximately 100°C and has a data output rate of 1 to 10 Hz. The probe is commonly used in studies of cloud microphysics and aircraft icing.

The Active Scattering Aerosol Spectrometer Probe (ASASP) is an airborne in-situ spectrometer made by Particle Measurement Systems, Inc. It measures the light intensity scattered by aerosol particles to determine particle size distribution and concentration. The wide-angle ASASP probes can detect light scattered between 35 and 120 degrees from the laser-beam axis.

The Precision Radiation Thermometer (PRT-5) is an in situ infrared temperature sensor. It makes non-contact infrared (8-14 μm) temperature measurements between -50 to 150 degrees Celsius with an accuracy of 0.5 degrees Celsius. It has a typical field of view of 2 degrees and a response time of either 0.3 Hz, 3 Hz, or 30 Hz. PRT-5 can be deployed on aircraft, vehicles, research vessels, and other ground-based platforms. It can be used for sea surface, ocean water, cloud, and air temperature measurements.

NOx/NOxy is an in situ chemiluminescence instrument that measures nitrogen oxides and ozone in the atmosphere. It offers a spatial resolution better than 100 meters at typical DC-8 research flight speeds. NOx/NOxy can be used on ground-based, airborne, and shipborne platforms, enabling it to support various atmospheric chemistry and air quality studies.

Rosemount Temperature Probes are in situ airborne temperature sensors manufactured by Rosemount, Inc. They provide atmospheric temperature measurements and are typically used to collect flight-level meteorological observations. Rosemount Temperature Probes consist of temperature transmitters, thermocouple sensors, resistance temperature detectors, and other temperature sensors.

Thermo Scientific Gas Analyzers are in situ gas analyzers manufactured by ThermoFisher Scientific. They provide precise measurements of various trace gases such as ozone, carbon dioxide, carbon monoxide, and sulfur dioxide. Thermo Scientific Gas Analyzers can be deployed on aircraft, research vessels, and ground-based platforms.

The Lyman-alpha Hygrometer is an in situ hygrometer designed for deployment on airborne or ground-based platforms. It measures water vapor absorption at the Lyman-alpha wavelength (121.6 nm) of atomic hydrogen to determine the total water content in the atmosphere. It has a detection limit of 0.1 ppmv and a typical data acquisition rate of 1 second. The Lyman-alpha hygrometer provides water vapor measurements with an accuracy of 6% and a precision of 5%.

The Forward Scattering Spectrometer Probe (FSSP) is an in situ airborne optical particle counter initially developed by Particle Measuring Systems, Inc. It determines particle size distribution by measuring the light intensity scattered by individual particles within the cloud. FSSP can detect particles ranging from 0.5 to 47 μm in diameter. It functions at a wavelength of 633 nm and typically samples at a rate of 1 Hz.

A pyrgeometer is a ground-based or airborne passive radiation sensor. It measures downward and upward longwave radiation in the 4-50 μm spectral range. Pyrgeometers measure changes in resistance/voltage using a thermopile sensor to determine longwave radiation. These measurements can be used to calculate the infrared radiation flux. Pyrgeometers are typically used for climatological, meteorological, and agricultural applications.

Video cameras capture video recordings of various phenomena for research purposes. They are used on aircraft to provide continuous views of weather and terrain below the flight path. Video cameras are also employed to verify the aircraft's flight track. Additionally, they are deployed at field sites to monitor changes in vegetation, land cover, clouds, air quality, glaciers, and other Earth science phenomena.

A pyranometer is a ground-based or airborne radiation sensor that measures solar irradiance across a hemispherical field of view. It detects the amount of solar energy reaching the surface, capturing both direct and diffuse sunlight. Pyranometers operate within a spectral range of 280-3000 nm. They are most commonly used for solar monitoring, climate research, weather forecasting, agriculture, and energy management.

The Modular Multiband Radiometer (MMR) is an airborne multispectral radiometer manufactured by Barnes Engineering Company. MMR measures radiance across 8 spectral bands in the infrared and visible wavelengths (0.4-12.5 μm) to produce images of vegetation and other surface features. At an altitude of 300 meters, the MMR has an instantaneous field of view (IFOV) of about 79 meters and a 15-degree field of view (FOV). It is typically deployed on small aircraft like helicopters but can also be used on ground-based platforms.

C-band scatterometers are active non-imaging scatterometers that measure microwave backscatter. They are typically used to measure ocean surface winds but can also be used to measure ice, vegetation, and soil surface properties. They operate in the C-band frequency range (4-8 GHz) and can provide measurements during the day and night.

The Spectron Engineering-590 (SE-590) Spectroradiometer is a portable spectroradiometer manufactured by Spectron Engineering. It can be used on both airborne and ground-based platforms. SE-590 uses a charge-coupled device (CCD) area array detector to measure reflectance. It operates across the visible to short-wave infrared spectral range (350-2500 nm). The SE-590 has a ground resolution of 4.5 meters when flown at an altitude of 300 meters.

Soil temperature sensors are in situ ground-based sensors used to measure and monitor soil temperature. They measure soil temperature by using thermistors or thermocouples to detect changes in resistance to calculate the temperature. Soil temperature sensors are used for agricultural purposes, environmental monitoring, and ecological research.

Sunphotometers are passive optical sensors that measure the amount of sunlight. They are pointed directly at the sun to measure direct sunlight and not sunlight scatter from aerosols. These measurements can be used to determine the aerosol optical depth by following Beer’s Law. Sunphotometers have been deployed on aircraft, research vessels, and field sites for aerosol research and monitoring.

The Sound Detection and Ranging (SODAR) is an active ground-based acoustic sensor that measures atmospheric winds and turbulence. It sends acoustic energy into the atmosphere and detects the strength and frequency of the backscattered energy. The backscattered signal can be used to determine the horizontal wind field, assuming the scattered energy moves with the mean wind. SODARs are frequently used in boundary layer studies to measure turbulence and wind profiles.

A pyranometer is a ground-based or airborne radiation sensor that measures solar irradiance across a hemispherical field of view. It detects the amount of solar energy reaching the surface, capturing both direct and diffuse sunlight. Pyranometers operate within a spectral range of 280-3000 nm. They are most commonly used for solar monitoring, climate research, weather forecasting, agriculture, and energy management.

The Volume Imaging Lidar (VIL) is a ground-based lidar system operated by the University of Wisconsin. It is an elastic backscatter lidar that operates at the 1064 nm wavelength. It provides aerosol backscatter profiles with a range resolution of 7.5 m or 15 m. VIL has a maximum range of 18 km and a repetition rate of 30 Hz. The Naval Research Laboratory (NRL) also operates its own VIL with similar specifications.

Generic-Atmospheric State (Gen-AtmsState) refers to non-specific instruments on a platform used for measurements of atmospheric state parameters. These are typically in situ sensors that measure temperature, pressure, humidity, and wind speed/direction. Types of atmospheric state instruments include thermometers, hygrometers, barometers, and anemometers.

Generic-Radiometers refer to non-specific radiometers on a platform. These are typically passive microwave radiometers that measure brightness temperature. Radiometers can be used to retrieve temperature and water vapor profiles, soil moisture content, ocean salinity, precipitation and cloud properties, and vegetation.

Eddy Covariance Flux Towers are in situ micrometeorological surface towers. They are equipped with gas sensors to continuously measure the trace gas fluxes between the land surface and the atmosphere. Eddy Covariance Towers are typically used to measure fluxes for carbon dioxide (CO2), methane (CH4), and water vapor (H2O). These towers are also equipped with various meteorological sensors to measure air temperature, precipitation, winds, radiation, and soil temperature.

The LI-COR Plant Canopy Analyzer is an in situ analyzer manufactured by LI-COR for leaf area index (LAI) measurements. It measures diffuse sky radiation that passes through the canopy across five zenith angels to determine LAI and other canopy characteristics. It can be used for most sky conditions and canopy types, such as row crops, grasslands, isolated trees, and forests. The optical sensor within the Plant Canopy Analyzer has a wavelength range of 320-490 nm. It has a field of view of 148 degrees and an operating temperature range of -20 to 50 degrees Celsius.

Digital cameras are used to provide imagery for research applications. Cameras are used on aircraft to collect aerial imagery for mapping and surveying, environmental monitoring, cloud observations, agriculture, geological studies, and other Earth science applications. They are also used at field sites to capture visual observations to monitor changes in land cover, vegetation, clouds, air quality, glaciers, and other phenomena.

The LI-COR Quantum Sensor is a ground-based, in situ radiation sensor manufactured by LI-COR. It collects precise photosynthetically active radiation (PAR) measurements beneath vegetation or under artificial light sources. The sensor detects radiation within the same light spectrum (400 - 700 nm) that plants use for photosynthesis. While primarily used for ground-based measurements, the LI-COR Quantum Sensor can also be mounted on aircraft. It is suitable for long-term deployments and remains durable in high temperatures and humidity conditions.

The Spectron Engineering-590 (SE-590) Spectroradiometer is a portable spectroradiometer manufactured by Spectron Engineering. It can be used on both airborne and ground-based platforms. SE-590 uses a charge-coupled device (CCD) area array detector to measure reflectance. It operates across the visible to short-wave infrared spectral range (350-2500 nm). The SE-590 has a ground resolution of 4.5 meters when flown at an altitude of 300 meters.

The Lyman-alpha Hygrometer is an in situ hygrometer designed for deployment on airborne or ground-based platforms. It measures water vapor absorption at the Lyman-alpha wavelength (121.6 nm) of atomic hydrogen to determine the total water content in the atmosphere. It has a detection limit of 0.1 ppmv and a typical data acquisition rate of 1 second. The Lyman-alpha hygrometer provides water vapor measurements with an accuracy of 6% and a precision of 5%.

Soil moisture probes are in situ ground-based sensors that measure soil water content. The most common type of soil moisture probes used for scientific research use dielectric permittivity techniques, such as capacitance or time-domain reflectometry sensors. These types of probes measure the charge-storage capacity of the soil to determine the soil moisture content. They typically operate at frequencies around 50 MHz and above to reduce sensitivity to salinity. Soil moisture probes provide continuous measurements and are relatively easy to deploy.

Rain gauges are ground-based instruments that measure liquid precipitation amounts directly over a specified period. Different rain gauges, such as tipping buckets and weighing gauges, collect and record data in various ways. Because of their small size and easy setup, rain gauges can be placed in different locations and are often used alongside other precipitation instruments like disdrometers to gather more details, such as precipitation rate and size distribution.

The Modular Multiband Radiometer (MMR) is an airborne multispectral radiometer manufactured by Barnes Engineering Company. MMR measures radiance across 8 spectral bands in the infrared and visible wavelengths (0.4-12.5 μm) to produce images of vegetation and other surface features. At an altitude of 300 meters, the MMR has an instantaneous field of view (IFOV) of about 79 meters and a 15-degree field of view (FOV). It is typically deployed on small aircraft like helicopters but can also be used on ground-based platforms.

Stream gauges are ground-based sensors that measure the water level or stage of rivers and streams at specific locations. The flow or discharge of a river can then be calculated from these stage measurements. These gauges can provide continuous data, making them useful for monitoring flood risk and water supply. The United States Geological Survey (USGS) operates a network of over 10,000 stream gauges across the United States to assist with flood prediction and water resource management.

The NOAA/WPL Pulsed Coherent Doppler Lidar is a ground-based lidar system developed by the NOAA Wave Propagation Laboratory (WPL). It measures radial velocity as a function of range using light-scattering particles in the air as tracers to derive wind profiles and momentum fluxes. It operates at a wavelength of 10.59 μm and has a pulse repetition rate from 1 to 20 Hz. It provides velocity azimuth display (VAD) scans, range height indication (RHI), and volume or roster scans at a range resolution of 150 meters.

The Portable Apparatus for Rapid Acquisition of Bidirectional Observations of the Land and Atmosphere (PARABOLA) is a passive ground-based sphere scanning radiometer. It measures surface reflectance across eight spectral channels. The first four channels (444, 551, 650, and 860 nm) coincide with spectral bands from the Multi-angle Imaging SpectroRadiometer (MISR) on the Terra satellite for validation purposes. The last four channels are used for the characterization of water vapor (944 nm), aerosol optical depth at longer wavelengths (1028 and 1650 nm), and measurements of photosynthetically active radiation (400-700 nm). The measurements from PARABOLA can be used to derive the surface bidirectional reflectance factor and sky and surface radiances. A complete scan of both sky and ground hemispheres takes approximately 3 minutes.

Soil temperature sensors are in situ ground-based sensors used to measure and monitor soil temperature. They measure soil temperature by using thermistors or thermocouples to detect changes in resistance to calculate the temperature. Soil temperature sensors are used for agricultural purposes, environmental monitoring, and ecological research.

Sunphotometers are passive optical sensors that measure the amount of sunlight. They are pointed directly at the sun to measure direct sunlight and not sunlight scatter from aerosols. These measurements can be used to determine the aerosol optical depth by following Beer’s Law. Sunphotometers have been deployed on aircraft, research vessels, and field sites for aerosol research and monitoring.

The Sound Detection and Ranging (SODAR) is an active ground-based acoustic sensor that measures atmospheric winds and turbulence. It sends acoustic energy into the atmosphere and detects the strength and frequency of the backscattered energy. The backscattered signal can be used to determine the horizontal wind field, assuming the scattered energy moves with the mean wind. SODARs are frequently used in boundary layer studies to measure turbulence and wind profiles.

A pyranometer is a ground-based or airborne radiation sensor that measures solar irradiance across a hemispherical field of view. It detects the amount of solar energy reaching the surface, capturing both direct and diffuse sunlight. Pyranometers operate within a spectral range of 280-3000 nm. They are most commonly used for solar monitoring, climate research, weather forecasting, agriculture, and energy management.

The Volume Imaging Lidar (VIL) is a ground-based lidar system operated by the University of Wisconsin. It is an elastic backscatter lidar that operates at the 1064 nm wavelength. It provides aerosol backscatter profiles with a range resolution of 7.5 m or 15 m. VIL has a maximum range of 18 km and a repetition rate of 30 Hz. The Naval Research Laboratory (NRL) also operates its own VIL with similar specifications.

Generic-Atmospheric State (Gen-AtmsState) refers to non-specific instruments on a platform used for measurements of atmospheric state parameters. These are typically in situ sensors that measure temperature, pressure, humidity, and wind speed/direction. Types of atmospheric state instruments include thermometers, hygrometers, barometers, and anemometers.

Generic-Radiometers refer to non-specific radiometers on a platform. These are typically passive microwave radiometers that measure brightness temperature. Radiometers can be used to retrieve temperature and water vapor profiles, soil moisture content, ocean salinity, precipitation and cloud properties, and vegetation.

Eddy Covariance Flux Towers are in situ micrometeorological surface towers. They are equipped with gas sensors to continuously measure the trace gas fluxes between the land surface and the atmosphere. Eddy Covariance Towers are typically used to measure fluxes for carbon dioxide (CO2), methane (CH4), and water vapor (H2O). These towers are also equipped with various meteorological sensors to measure air temperature, precipitation, winds, radiation, and soil temperature.

The LI-COR Plant Canopy Analyzer is an in situ analyzer manufactured by LI-COR for leaf area index (LAI) measurements. It measures diffuse sky radiation that passes through the canopy across five zenith angels to determine LAI and other canopy characteristics. It can be used for most sky conditions and canopy types, such as row crops, grasslands, isolated trees, and forests. The optical sensor within the Plant Canopy Analyzer has a wavelength range of 320-490 nm. It has a field of view of 148 degrees and an operating temperature range of -20 to 50 degrees Celsius.

Digital cameras are used to provide imagery for research applications. Cameras are used on aircraft to collect aerial imagery for mapping and surveying, environmental monitoring, cloud observations, agriculture, geological studies, and other Earth science applications. They are also used at field sites to capture visual observations to monitor changes in land cover, vegetation, clouds, air quality, glaciers, and other phenomena.

The LI-COR Quantum Sensor is a ground-based, in situ radiation sensor manufactured by LI-COR. It collects precise photosynthetically active radiation (PAR) measurements beneath vegetation or under artificial light sources. The sensor detects radiation within the same light spectrum (400 - 700 nm) that plants use for photosynthesis. While primarily used for ground-based measurements, the LI-COR Quantum Sensor can also be mounted on aircraft. It is suitable for long-term deployments and remains durable in high temperatures and humidity conditions.

The Spectron Engineering-590 (SE-590) Spectroradiometer is a portable spectroradiometer manufactured by Spectron Engineering. It can be used on both airborne and ground-based platforms. SE-590 uses a charge-coupled device (CCD) area array detector to measure reflectance. It operates across the visible to short-wave infrared spectral range (350-2500 nm). The SE-590 has a ground resolution of 4.5 meters when flown at an altitude of 300 meters.

The Lyman-alpha Hygrometer is an in situ hygrometer designed for deployment on airborne or ground-based platforms. It measures water vapor absorption at the Lyman-alpha wavelength (121.6 nm) of atomic hydrogen to determine the total water content in the atmosphere. It has a detection limit of 0.1 ppmv and a typical data acquisition rate of 1 second. The Lyman-alpha hygrometer provides water vapor measurements with an accuracy of 6% and a precision of 5%.

Soil moisture probes are in situ ground-based sensors that measure soil water content. The most common type of soil moisture probes used for scientific research use dielectric permittivity techniques, such as capacitance or time-domain reflectometry sensors. These types of probes measure the charge-storage capacity of the soil to determine the soil moisture content. They typically operate at frequencies around 50 MHz and above to reduce sensitivity to salinity. Soil moisture probes provide continuous measurements and are relatively easy to deploy.

Infrared Thermometers (IRTs) are ground-based pyrometers that measure the brightness temperature of a scene within their field of view. They determine brightness temperature by detecting electromagnetic radiation emitted by Earth’s surface. These measurements are used to find either the surface skin temperature or the sea surface temperature, depending on whether the platform is on land or water. IRTs typically operate within the 8- to 14-μm wavelength range.

Rain gauges are ground-based instruments that measure liquid precipitation amounts directly over a specified period. Different rain gauges, such as tipping buckets and weighing gauges, collect and record data in various ways. Because of their small size and easy setup, rain gauges can be placed in different locations and are often used alongside other precipitation instruments like disdrometers to gather more details, such as precipitation rate and size distribution.

The Modular Multiband Radiometer (MMR) is an airborne multispectral radiometer manufactured by Barnes Engineering Company. MMR measures radiance across 8 spectral bands in the infrared and visible wavelengths (0.4-12.5 μm) to produce images of vegetation and other surface features. At an altitude of 300 meters, the MMR has an instantaneous field of view (IFOV) of about 79 meters and a 15-degree field of view (FOV). It is typically deployed on small aircraft like helicopters but can also be used on ground-based platforms.

Stream gauges are ground-based sensors that measure the water level or stage of rivers and streams at specific locations. The flow or discharge of a river can then be calculated from these stage measurements. These gauges can provide continuous data, making them useful for monitoring flood risk and water supply. The United States Geological Survey (USGS) operates a network of over 10,000 stream gauges across the United States to assist with flood prediction and water resource management.

The Portable Apparatus for Rapid Acquisition of Bidirectional Observations of the Land and Atmosphere (PARABOLA) is a passive ground-based sphere scanning radiometer. It measures surface reflectance across eight spectral channels. The first four channels (444, 551, 650, and 860 nm) coincide with spectral bands from the Multi-angle Imaging SpectroRadiometer (MISR) on the Terra satellite for validation purposes. The last four channels are used for the characterization of water vapor (944 nm), aerosol optical depth at longer wavelengths (1028 and 1650 nm), and measurements of photosynthetically active radiation (400-700 nm). The measurements from PARABOLA can be used to derive the surface bidirectional reflectance factor and sky and surface radiances. A complete scan of both sky and ground hemispheres takes approximately 3 minutes.

The Modular Multiband Radiometer (MMR) is an airborne multispectral radiometer manufactured by Barnes Engineering Company. MMR measures radiance across 8 spectral bands in the infrared and visible wavelengths (0.4-12.5 μm) to produce images of vegetation and other surface features. At an altitude of 300 meters, the MMR has an instantaneous field of view (IFOV) of about 79 meters and a 15-degree field of view (FOV). It is typically deployed on small aircraft like helicopters but can also be used on ground-based platforms.

C-band scatterometers are active non-imaging scatterometers that measure microwave backscatter. They are typically used to measure ocean surface winds but can also be used to measure ice, vegetation, and soil surface properties. They operate in the C-band frequency range (4-8 GHz) and can provide measurements during the day and night.

The Spectron Engineering-590 (SE-590) Spectroradiometer is a portable spectroradiometer manufactured by Spectron Engineering. It can be used on both airborne and ground-based platforms. SE-590 uses a charge-coupled device (CCD) area array detector to measure reflectance. It operates across the visible to short-wave infrared spectral range (350-2500 nm). The SE-590 has a ground resolution of 4.5 meters when flown at an altitude of 300 meters.

Spectrometers are instruments used to separate and analyze the spectral components of a substance. They usually measure the electromagnetic radiation that has been reflected, absorbed, or transmitted by the physical sample. Spectrometers can operate across the ultraviolet to infrared spectrum. The most common types include optical, nuclear magnetic resonance, and mass spectrometers. They can be used on aircraft, research vessels, vehicles, and other ground-based platforms.

Infrared Thermometers (IRTs) are ground-based pyrometers that measure the brightness temperature of a scene within their field of view. They determine brightness temperature by detecting electromagnetic radiation emitted by Earth’s surface. These measurements are used to find either the surface skin temperature or the sea surface temperature, depending on whether the platform is on land or water. IRTs typically operate within the 8- to 14-μm wavelength range.