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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/220357
A Comprehensive Validation of Global Precipitation Measurement Satellite Products Over a Western Mediterranean Region
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[eng] Precipitation estimation is essential for understanding atmospheric processes, water resource management, and climate modeling. Advances in remote sensing, particularly the Global Precipitation Measurement (GPM) mission, have improved global precipitation coverage, especially in regions where traditional methods are insufficient. Since its launch in 2014, GPM has become one of the most comprehensive efforts to quantify precipitation globally, with continuous updates to its products. The complex Mediterranean climate, characterized by high variability and uncertainty in precipitation projections, highlights the importance of validating these products. This thesis focuses on validating GPM precipitation estimates over a Western Mediterranean region.
The thesis is structured into three parts, based on three scientific publications and a preprint. It begins with the validation of Integrated Multi-satellite Retrievals for GPM (IMERG) products across multiple temporal scales, particularly their performance in detecting intense rainfall in the Mediterranean. The impact of cloud top phase on satellite retrievals is also examined through 18 case studies, along with a comparison to Support to Operational Hydrology and Water Management (H SAF) products. Finally, rain estimates and drop size distributions from the GPM Dual-frequency Precipitation Radar (DPR) are validated.
Many GPM validation studies lack evaluations at sub-daily scales or in mountainous regions. This thesis addresses these gaps by assessing IMERG Early, Late, and Final runs at different temporal scales in Catalonia, using ground stations from 2015 to 2020. While IMERG Final reduces errors at all scales, it underestimates precipitation in areas like the Pyrenees, and both Early and Late runs tend to overestimate rainfall. IMERG also shows high bias and low correlation at sub-daily scales, indicating challenges in estimating precipitation at high temporal resolution. Very heavy rainfall is significantly underestimated, by more than 80%.
The second part of the study focuses on extreme precipitation events, using IMERG Early and Late products to assess retrievals’ performance. Stratified results based on the microphysical properties of clouds show a general underestimation of precipitation, which worsens with increased rainfall intensity and temporal resolution. Passive microwave (PMW) sensors showed less bias than infrared (IR) sensors, although including IR increased errors. IMERG performed better in ice-phase clouds compared to warm and mixed-phase clouds.
This analysis was extended to compare IMERG with H SAF products in 18 extreme rainfall cases, using a pixel-to-point approach to reduce discrepancies between satellite and ground data. H64 performed best at daily scales, and H68 at hourly detection, although accuracy decreased with increasing rainfall intensity. Despite biases, the IMERG Late product was the most effective at detecting extreme precipitation events.
The final part of the thesis evaluates the GPM Core satellite’s Dual-frequency Precipitation Radar (DPR), focusing on seven disdrometers in various topographic regions from 2014 to 2023. Radar reflectivity, drop size distributions, and precipitation intensity were compared. GPM DPR captured variability in observed drop size distributions but overestimated the mass-weighted mean diameter and underestimated the
intercept parameter. Errors were highest for rainfall rate and the intercept parameter, but lowest for radar reflectivity and the mass-weighted mean diameter. The classification of stratiform and convective rainfall by GPM DPR also showed an overestimation of stratiform cases.
This research is one of the first in the Iberian Peninsula to validate IMERG products with a detailed focus on orographic, climatic, and precipitation intensity factors at high temporal resolution. By comparing GPM and H SAF products and evaluating updates to DPR version 7, this study provides valuable insights into satellite precipitation estimation and lays the foundation for future research.
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PEINÓ CALERO, Eric. A Comprehensive Validation of Global Precipitation Measurement Satellite Products Over a Western Mediterranean Region. [consulta: 29 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/220357]