Cloud Profile and Rain Radars
Instrument Types
Because of its unyielding power over our livelihoods, humans around the globe and through the ages have devised ways of studying and forecasting weather. This need is becoming ever greater due to the increasing impact of extreme weather events, often driven or accentuated by significant precipitation. 1) 2) 3)
The ability to make weather observations has developed significantly in recent years, to the point where we now have an intricate network of instruments, including ground-based radar, weather balloons, and satellites. Using these tools we are able to, at a global scale, quantitatively observe patterns of weather such as the shape, extent, and behaviour of clouds and rain, and thus make statistical predictions of the likelihood of near- and mid-future weather scenarios. 4) 5)
Rain Radar
The discovery that radar could be used to detect rain occurred during the first World War, after frustrations that radar dishes designed to detect enemy aircraft functioned poorly in heavy rain, leaving large spots on the radar maps where the rain was present. After the war, surplus radars were positioned around the USA, forming a large-scale network of rain radars that could give early warnings of developing storms. Over the 20th century, these were developed and rebuilt in order to specifically function as meteorological radars (Figure 1). Two of the most important developments by the National Oceanographic and Atmospheric Administration (NOAA) in this field were the development of the Phased Array Radar (PAR) and the Dual-Polarised Weather Radar (DUAL-POL). While the traditional radars were limited by their mechanical movements, refreshing on one area only every few minutes, PAR could be steered electronically, allowing the radar beam to be pointed at areas of interest, thus giving more up-to-date information on storms. DUAL-POL emits radar beams that are polarised both horizontally and vertically with respect to the ground. This allows the 3D structure of precipitation particles to be determined, which further allows the discrimination of different particle types, such as snow, ice, rain, or hail. In addition, DUAL-POL can differentiate between precipitation and other objects, such as birds or flying debris. 6)
Rain can also be observed from space-based instruments. The Tropical Rainfall Measuring Mission (TRMM) was the first space-based radar capable of measuring rainfall, operating from 1997 - 2015. TRMM provided invaluable information for understanding tropical and subtropical rainfall, one of the most important, but least understood, parameters in global change. TRMM was followed by the Global Precipitation Mission, which uses a network of satellites designed to unify and advance precipitation measurements from research and operational microwave sensors for delivering next-generation global precipitation data products. By staggering local overpass times, the constellation of GPM satellites provide high quality estimates of Earth’s rain and snowfall every 30 minutes. 7) 8)
Cloud Profiles
Clouds are an essential part of the climate system, and so it is essential to understand them. However, they can be difficult to measure and observe. Clouds typically obscure electromagnetic radiation, and when they are thick it can be difficult to obtain information on all layers. In addition, cloud-base, an important feature of clouds, cannot be measured from space. Clouds are classified according to the World Meteorological Organisation standardised criteria. They are typically referred to by their ‘Genus’ and ‘species’, and whether they are high, medium, or low (the exact height of which varies depending on location). 9)
A significant development in the observation of clouds came from the deployment of spaceborne lidar sensors, such as the CALIOP instrument on the CALIPSO satellite. Lidar emits short laser pulses and times their return to generate a 3D map of the target area. As lasers can mostly travel through clouds, the returning backscatter can provide vertical distribution maps, or profiles. Other sensors used in cloud assessments include multi-spectral imagers, infrared (IR) sounders, multi-angle, multi-spectral imagers, limb sounders, and passive microwave imagers. Different sensors have different advantages and limitations. For example, IR sounders are useful for the reliable identification of cirrus both during the daytime and nighttime. 10) 11)
Example Products
Lidar cloud profiles
Lidar functions by emitting laser pulses and measuring both the intensity of backscatter and the time it takes for the laser to return to the instrument. This data gives information on the qualities of the object being observed and the distance of the object from the sensor. Through this, high-resolution three-dimensional maps can be created of a target area, including clouds. Atmospheric lidar data are commonly displayed in ‘lidar curtains’, which are concurrent strips of cross-sectional profiles of atmospheric composition. These can be correlated into a more complete map of the extent and behaviour of observed clouds. 12) 13)
Precipitation profiles
Radar data from satellites can be presented as global grids of Level 3 data. Instantaneous precipitation estimates from Level 2 retrieval algorithms are accumulated into grids over a specified time span. Each grid may include data on the number of measurements, mean, and standard deviation. 14)
CLARA-A1 (Cloud, Albedo, and Radiation dataset, AVHRR-based, version 1)
CLARA-A1 is a global dataset of cloud properties, surface albedo, and surface radiation products, generated by the EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) (Figure 7). Data from the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA and MetOp (Meteorological Operational Satellite) satellites are used to derive the products, which are available over numerous timescales from 1982 to 2009. 15)
Related Missions
GPM (Global Precipitation Measurement) Mission
The GPM (Global Precipitation Measurement) Mission is an international US/Japanese multi-satellite constellation with the prime agencies being NASA (National Aeronautics and Space Administration) and JAXA (Japanese Aerospace Exploration Agency). The constellation’s primary spacecraft, GPM Core Observatory (built by NASA), was launched in February 2014, joining a collaboration of 12 GPM satellites, aiming to study global precipitation, evaporation and the water cycle. GPM Core Observatory carries the active microwave DPR (Dual-frequency Precipitation Radar) and the passive microwave GMI (GPM Microwave Imager).
EarthCARE (Earth Clouds, Aerosols and Radiation Explorer)
EarthCARE is operated by JAXA and ESA, and will develop climate and weather forecasting models by understanding the role of cloud-aerosol-radiation interactions. The Atmospheric Lidar (ATLID) provides vertical profiles of aerosols and thin clouds, while the Cloud Profiling Radar (CPR) provides vertical profiles of thicker clouds.
TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats)
TROPICS is a constellation of four 3U CubeSats launched in May 2023 (plus a pathfinder launched in June 2021) operated by NASA. Each CubeSat is equipped with a microwave spectrometer, which measures temperature, humidity, and precipitation.
TRMM (Tropical Rainfall Measuring Mission)
A research satellite developed jointly by NASA and JAXA, TRMM was a part of NASA’s ESE program and carried a variety of instruments that gathered information about precipitation and latent heating between the tropics of Capricorn and Cancer, to further our understanding of global energy, water cycles, and climate.
CloudSat
Led by NASA and assisted by the Canadian Space Agency (CSA) and the United States Department of Defence (DoF), CloudSat functions to collect data on clouds and thus improve the way clouds are represented in global models and the accuracy of cloud activity predictions.
CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)
Launched April 2006, CALIPSO makes observations that are used to determine the role of clouds and aerosols in regulating the Earth’s climate, including the use of LiDAR to construct 3D models of cloud structure. It is operated by NASA and CNES (Centre National D’Etudes Spatiales, France).
INCUS (INvestigation of Convective UpdraftS)
INvestigation of Convective UpdraftS (INCUS) is a mission composed of 3 SmallSats each carrying a Ka-band radar, funded and developed by NASA-JPL (Jet Propulsion Laboratory) alongside Colorado State University. The three SmallSats will be flown in close succession (30, 90, and 120 seconds apart from each other), which will allow for a novel time-differencing approach to be used for the first time to estimate convective mass flux in tropical convective storms.
Aqua
A jointly funded mission by NASA (National Aeronautics and Space Administration, USA), INPE (National Institute for Space Research, Brazil), and JAXA (Japan Aerospace Exploration Agency, Japan), launched in May 2002, Aqua (formerly known as EOS/PM-1) is part of NASA’s international Earth Observing System (EOS), and their Earth Science Enterprise (ESE) program. Aqua contributes to the multidisciplinary study of the Earth’s water cycle, which includes observations on cloud extent and precipitation.
GOES-R (Geostationary Operational Environmental Satellite-R)
GOES-R is a series of geostationary weather monitoring satellites operated by the National Oceanic and Atmospheric Administration (NOAA) and NASA. It was launched November 2016 and provides high-resolution imagery and radiometric information of cloud cover, as well as measurements of lightning activity and ice-phase precipitation.
JPSS-2 (Joint Polar Satellite System-2)
JPSS is a collaborative program between NOAA and NASA as part of NOAA’s POES (Polar-Orbiting Environmental Satellites) system. JPSS-2 is the second mission of POES and features several instruments that provide observations of atmospheric, terrestrial, and oceanic conditions for the purposes of both weather forecasting and long-term climate and environmental data records. It is one of five satellites in the JPSS constellation, alongside JPSS-1, Suomi NPP, JPSS-3, and JPSS-4.
Suomi NPP (Suomi National Polar-Orbiting Partnership)
Launched October 2011, Suomi NPP is a weather satellite aimed at monitoring the Earth’s environment and climate. It is operated by NASA and NOAA.
References
1) “HURRICANE IAN (AL092022),” National Hurricane Center Tropical Cyclone Report, NOAA, April 2023, URL:https://www.nhc.noaa.gov/data/tcr/AL092022_Ian.pdf
2) “Understanding Droughts,” National Geographic, October 2023, URL:https://education.nationalgeographic.org/resource/understanding-droughts/
3) “Weather tracker: deaths after first heavy snowfall of winter hits eastern Europe,” Alice Fowle, The Guardian, December 2023, URL:https://www.theguardian.com/world/2023/dec/01/weather-tracker-deaths-heavy-snowfall-winter-eastern-europe
4) “Weather Forecasting Through the Ages,” Earth Observatory, NASA, February 2002, URL:https://earthobservatory.nasa.gov/features/WxForecasting/wx2.php
5) “Indigenous Weather Knowledge,” Australian Government Bureau of Meteorology, 2016, URL:http://www.bom.gov.au/iwk/
6) “Research Tools: Radar,” National Severe Storms Laboratory, NOAA, URL:https://www.nssl.noaa.gov/tools/radar/
7) “TRMM (Tropical Rainfall Measuring Mission),” EO Portal, ESA, June 2012, URL:https://www.eoportal.org/satellite-missions/trmm#space-and-hardware-components
8) “The GPM Constellation”, NASA, URL: https://gpm.nasa.gov/missions/GPM/constellation
9) “How we measure cloud,” Met Office, URL: https://www.metoffice.gov.uk/weather/guides/observations/how-we-measure-cloud
10) “The Climate Data Guide: Cloud Dataset Overview,” Stubenrauch Claudia & National Center for Atmospheric Research Staff (Eds), September 2022, URL:https://climatedataguide.ucar.edu/climate-data/cloud-dataset-overview
11) “Climate Data Guide Spurs Discovery and Understanding,” Schneider D.P., et al., EOS, Transactions American Geophysical Union, Vol. 94, issue 13, pp. 121-122, URL:https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2013EO130001
12) “Lidar (Light detection and ranging),” EoPortal, ESA, July 2023, URL:https://www.eoportal.org/other-space-activities/lidar
13) “CALIPSO Quality Statements: Lidar Level 2 Cloud and Aerosol Profile Products Version Releases: 3.01, 3.02,” Atmospheric Science Data Center, URL:https://asdc.larc.nasa.gov/documents/calipso/quality_summaries/CALIOP_L2ProfileProducts_3.01.pdf
14) Toshio Iguchi, Robert Meneghini (2021), “GPM DPR Precipitation Profile 1 month 0.25 degree x 0.25 degree V07”, Greenbelt, MD, Goddard Earth Sciences Data and Information Services Center (GES DISC), https://disc.gsfc.nasa.gov/datasets/GPM_3DPR_07/summary
15) “The Climate Data Guide: CLARA-A1: Cloud properties, surface albedo and surface radiation products based on AVHRR,” Stengel Martin & National Center for Atmospheric Research Staff (Eds), September 2022, URL:https://climatedataguide.ucar.edu/climate-data/clara-a1-cloud-properties-surface-albedo-and-surface-radiation-products-based-avhrr