PERSIANN (Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks) is G-WADI’s flagship decision-support product. It and the other related products and tools described in this section were developed by the Center for Hydrometeorology and Remote Sensing (CHRS) of the University of California, Irvine. PERSIANN is a satellite-based precipitation retrieval algorithm, providing near-real time precipitation products (Hsu et al., 1997; Sorooshian et al., 2000). It uses an adaptive neural network algorithm to combine information from various satellites. This includes high frequency (48 readings a day) geosynchronous satellite based gridded infrared images and low frequency (1–2 readings a day) instantaneous rain derived from the TRMM TMI microwave imager (Hughes et al., 2006; Brown et al., 2006). The adaptive neural network means that the product can be adapted and calibrated flexibly for different precipitation regimes (Asadullah et al., 2008).
The original PERSIANN product has a temporal resolution of 1 hour and a global spatial grid of 0.25° between 60°N and 60°S.
Additionally, a Cloud Classification System (PERSIANN-CCS, Hong et al., 2004; Hsu et al., 2013) algorithm is available at spatial and temporal resolutions of 0.04° and 1h, respectively. The CCS algorithm is optimized for observing extreme precipitation, particularly at very high spatial resolution. Typical applications include flood forecasting, hydrological modelling, drought monitoring, and soil moisture analysis.
A third product, PERSIANN-CDR is a retrospective satellite-based climate data record starting on 1 January 1983. It is aimed at hydrological and climate studies that require longterm consistent data, for instance for trend and risk analysis (Ashouri et al., 2015).
For all PERSIANN products, user-friendly interfaces exist. For example, iRain is a web-based graphical interface to near real-time PERSIANN-CCS data, and an iRain mobile app is available for iOS and Android devices under the name “iRain UCI”. RainSphere is a system based on PERSIANN-CDR that allows the user to visualize and analyse historical and future precipitation at a variety of spatial and temporal scales (Nguyen et al., 2016).
Data for PERSIANN, PERSIANN-CCS and PERSIANN-CDR are all easily downloadable from the CHRS Data Portal.