## 2 Materials and Methods
### Methodology
#### 2.2.1 Phase 1: Data Acquisition  
Rain gauge observations were acquired from the Department of Irrigation and Drainage (DID), Malaysia. The data were used as a comparison and for training purposes for the  
Figure 3: Methodology flow chart.  
Figure 2: Schematic diagram of the relational database constructed using various technologies in connection with further research.  
satellite rainfall data. The distribution of rain gauge observations is presented in Figure 1. Satellite rainfall data can be acquired from the respective agencies' webpages. For example, TRMM and IMERG satellite files can be acquired from the Goddard Earth Sciences Data and Information Services Centre (GES DISC) ([[https://disc.gsfc.nasa.gov/](https://disc.gsfc.nasa.gov/)]([https://disc.gsfc.nasa.gov/](https://disc.gsfc.nasa.gov/)) (accessed on 15 June 2021)), and PERSIANN satellite files can be obtained from the portal of the Center for Hydrometeorology and Remote Sensing (CHRS) ([[https://chrsdata.eng.uci.edu/](https://chrsdata.eng.uci.edu/)]([https://chrsdata.eng.uci.edu/](https://chrsdata.eng.uci.edu/)) (accessed on 30 September 2021)). Before the satellite files were downloaded, CentOS Linux ([[https://www.centos.org/](https://www.centos.org/)]([https://www.centos.org/](https://www.centos.org/)) (accessed on 10 June 2021)) was set up. CentOS is a freely available computing platform that serves as an ideal environment for executing command-line utilities such as the Wget computer program, which enables the seamless retrieval of files from the Internet. As it is open source, and community-supported, CentOS Linux is a rich base platform that provides a consistent, manageable platform for various deployments. Due to the vast number of files involved, we developed Shell Scripts incorporating the Wget program to facilitate the retrieval of IMERG satellite files in a batch processing manner. These IMERG satellite files are in Hierarchical Data Format version 5 (HDF5) format which is the standard mechanism for storing large quantities of numerical data [62].  
The current research focuses on the Integrated Multi-Satellite Retrievals for Global (IMERG) precipitation measurement [18]. IMERG is an estimation that combines data from the Global Precipitation Measurement (GPM) satellite constellation to predict precipitation, which is particularly important over the majority of the Earth's surface that lacks precipitation-measuring instruments on the ground. Lately, with the IMERG Version 6, the algorithm merged the TRMM satellite's operation (2000-2015) with the GPM satellite (2014-present). These products have improvements in terms of coverage (60\({}^{\circ}\) N-60\({}^{\circ}\) S) as well as spatial (0.1\({}^{\circ}\)) and temporal (30 min) resolutions. In addition to the higher spatial-temporal resolution, IMERG provides three runs which are IMERG Early (IMERG-E), IMERG Late (IMERG-L), and IMERG Final (IMERG-F), to accommodate various consumer requirements for latency and accuracy. For the present study, the IMERG-F 30 min interval product at a spatial resolution of 0.1\({}^{\circ}\) was employed as it had been bias-corrected using the Global Precipitation Climatology Centre (GPCC) precipitation gauges and is suitable for scientific research.