كليدواژه :
ماهواره‌هاي GPM و SMAP , بارش , رطوبت خاك , سيل
چكيده فارسي :
ماهواره فعال/غيرفعال رطوبت خاك ((SMAP، براي نقشه‌برداري و پايش رطوبت سطحي خاك توسعه يافته است و در نقشه‌برداري طغيان رودخانه‌ها استفاده مي‌شود. ازطرف‌ديگر، مأموريت اندازه‌گيري جهاني بارش (GPM)، اولين ماهواره‌اي است كه هدف آن اندازه‌گيري بارش باران و برف سبك و همچنين باران‌هاي شديد حاره‌اي است. بازيابي‌هاي يكپارچه چند‌ماهواره‌اي براي GPM (IMERG)، برآوردهاي شبه‌كره‌اي (°N60-°S60) از بارش را فراهم مي‌آورد.
در اين مطالعه، تخمين بارش روزانه سه اجراي IMERG (نسخه 4) با داده‌هاي بارش 22 ايستگاه همديدي سازمان هواشناسي كشور واقع در شمالغرب و غرب ايران، براي دوره آوريل 2016 تا فوريه 2017 مقايسه مي‌شوند. كميت‌هاي راست‌آزمايي براي دو آستانه وقوع بارش (mm/day 1/0) و نيز بارش‌هاي متوسط يا بيشتر (mm/day 5) محاسبه شدند. نتايج، فروتخمين اين سه اجرا (محصولات) را براي بارش‌هاي بيشتر از mm/day 5 نشان مي‌دهند، اگرچه ميزان اين فروتخمين براي محصول IMERG-F نسبت به دو محصول ديگر كمتر است. همچنين در آستانه دوم، احتمال آشكارسازي (POD) و امتياز مهارتي پيرس (PSS) بيانگر كارايي بهتر محصول IMERG-F نسبت به دو محصول ديگر است. كميت‌هاي نسبت هشدارهاي نادرست (FAR) و احتمال آشكارسازي نادرست (POFD) براي هر سه محصول تقريباً يكسان است. به‌علاوه، در اين تحقيق با استفاده از اين دو سامانه ماهواره‌اي، نقشه‌برداري ماهواره‌اي سيل شديد در شمالغرب ايران در 14 آوريل 2017 (25 فروردين 1396) انجام شده است. مطابقت تغييرات محصول رطوبت خاك حاصل از SMAP با سامانه بارشي آشكارسازي شده توسط GPM، دلالت بر امكان استفاده عملياتي تركيبي اين دو مأموريت براي ارزيابي و پايش سيل دارد.
چكيده لاتين :
Soil moisture influences the partitioning of rainfall into evapotranspiration, infiltration and runoff, hence it is an important factor for determining the magnitude of flood events. The Soil Moisture Active and Passive (SMAP) mission is a microwave all-weather sensor with cloud penetration capability it can be harnessed for inundation mapping. On the other hand, Global Precipitation Measurement (GPM) is the first satellite that has been designed to measure light rain and snowfall, in addition to heavy tropical rainfall. The Integrated Multi-satellitE Retrievals for GPM (IMERG) products, with 0.1° × 0.1° spatial resolution and 30 min temporal resolution, are available in the form of near-real-time data, i.e., IMERG Early and Late, and in the form of post-real-time research data, i.e., IMERG Final, after monthly rain gauge analysis is received and taken into account.
In this study, daily rainfall estimates from IMERG Early, Late, and Final runs (IMERG-E, IMERG-L and IMERG-F) are compared with daily precipitation measured by 22 synoptic rain-gauges over the northwest and western regions of Iran. Assessment is implemented for a period from April 2016 to February 2017. The assessment technique is using a contingency table that reflects the frequency of “Yes” and “No” of the satellite estimation. We have used two threshold values of 0.1 mm/day to define rain/no rain and 5.0 mm/day as moderate or higher rainfall events. The scatter plots of daily precipitation values, IMERG-E, IMERG-L and IMERG-F data against rain-gauge observations, indicate underestimation according to Bias for moderate or higher rainfall; this is more so when the precipitation threshold is increased. However, the IMERG-F shows better performance (i.e., closer to one-to-one line) in estimating moderate or higher rain. For the first threshold, all the three runs show approximately same performances; but some differences are seen at the second threshold. At this threshold, POD for IMERG-F is about 0.27 and for the two other products is about 0.14, which means larger fraction of the observed “Yes” events was correctly estimated by IMERG-F than IMERG-E and IMERG-L.
At the second part of this work, the synergistic use of satellite-based precipitation and soil moisture observations was dedicated to mapping of flood monitoring in the northwest of Iran on 14 April 2017. In this study, a value-added product was used that over-samples the SMAP volumetric soil moisture data with a spatial resolution of 40 km and posts it on a 9 km grid, SPL2SMP_E. The SMAP data maps show a pattern that is consistent with the precipitation maps; i.e., following the rainfall on 14 April, there is an increase in the saturated area and after that it begins to decay.
So together, SMAP and GPM can provide information on the surface water fluxes, an important quantity for assessing and monitoring the Earth’s fresh water resources. Therefore, integrated GPM and SMAP data can serve as a key tool for application users and emergency management to assess the extent and potential impact of flooding events among other hydrometeorological phenomena.
