# Satellite Remote Sensing of Precipitation and the Terrestrial Water Cycle in a Changing Climate
## 3 Satellite Measurement of Precipitation  
A general improvement of the observational capabilities for the constant monitoring of precipitation will substantially contribute to the investigation of climate change processes. Measuring precipitation from space has been a key application of passive remote sensing since the early days of satellite meteorology in the 1960s.  
Several review articles deal with satellite precipitation measurements on various levels and from different perspectives [(88; 89; 90; 91; 92; 93; 94; 95; 96; 97)]. Science principles, algorithms, initial validation efforts, and new missions were described in Levitzani et al. [(98)]. A new comprehensive presentation of the state of the art of satellite precipitation measurements is now being published, describing the status of observations and satellite programs, retrieval techniques, algorithms and sensors, and validation programs worldwide, as well as the observed characteristics of precipitation processes, and applications that have recently developed from the wealth of satellite precipitation products [(99)]. The evolution of satellite observational capabilities in recent times is shown in Figure 5. Hereafter, science and technology advancements and critical aspects of the available products are discussed.  
The need for measuring precipitation from space stems from a few key considerations:  
* Raingauges are not evenly distributed, and cover a very limited portion of the Earth [(100)]. However, global gridded products are available from a variety of sources, such as, for example, the GPCC [(1)], the Global Historical Climatology Network (GHCN, [(101)]), and the recent Rainfall Estimates on a Gridded Network (REGEN, [(102)]).
* Radar networks are generally deployed by developed countries ([[http://wrd.mgm.gov.tr/default.aspx?l=en](http://wrd.mgm.gov.tr/default.aspx?l=en)]([http://wrd.mgm.gov.tr/default.aspx?l=en](http://wrd.mgm.gov.tr/default.aspx?l=en)), last accessed 21 August 2019). Datasets for water cycle studies are becoming available over limited areas, such as the Multi-Radar/Multi-Sensor System (MRMS; [[https://www.nssl.noaa.gov/projects/mrms/](https://www.nssl.noaa.gov/projects/mrms/)]([https://www.nssl.noaa.gov/projects/mrms/](https://www.nssl.noaa.gov/projects/mrms/)), last accessed 24 September 2019) developed by the National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory (NSSL) [(103)].  
Figure 5: Evolution of the satellite constellation for precipitation measurements.  
and the Nimrod data system for UK and Western Europe ([[https://catalogue.ceda.ac.uk/uuid/82](https://catalogue.ceda.ac.uk/uuid/82) adec1f896 af6169112d09 cc1174499]([https://catalogue.ceda.ac.uk/uuid/82](https://catalogue.ceda.ac.uk/uuid/82) adec1f896 af6169112d09 cc1174499), last accessed 25 September 2019) developed by the UK Met Office.
* Oceans are not fully covered, apart from scattered ship observations, buoys, and radars on small islands which have been made available through the International Comprehensive Ocean-Atmosphere Data Set (ICOADS, [104]), the Global Summary of the Day (GSOD, [105]), the Pacific Rainfall Database (PACRAIN, [106; 107]), and ship-based measurement campaigns, such as the Ocean Rain And Ice-phase precipitation measurement Network (OceanRAIN, [108]).