Satellite Altimetry and Hydrologic Modeling of Poorly-Gauged Tropical Watershed by Yohanes Budi Sulistioadi Report No. 505 Geodetic Science The Ohio State University Columbus, Ohio 43210 November 2013 SATELLITE ALTIMETRY AND HYDROLOGIC MODELING OF POORLY-GAUGED TROPICAL WATERSHED By Yohanes Budi Sulistioadi Report No. 505 Geodetic Science The Ohio State University Columbus, Ohio 43210 November 2013 Copyright by Yohanes Budi Sulistioadi 2013 Preface This report was prepared for and submitted to the Graduate School of the Ohio State University as a dissertation for partial fulfillment of the requirements for the Doctor of Philosophy (PhD) degree. This research was carried out under supervision of Professor C.K. Shum, Division of Geodetic Science, School of Earth Sciences, The Ohio State University. Hidayat at Hydrology and Quantitative Water Management Department of Wageningen University and Limnology Research Agency of Indonesian Institute of Sciences (LIPI) are especially acknowledged for providing in-situ discharge, rating curve and precipitation data for the Upper Mahakam Sub-watershed study region. This research is primarily supported by the Fulbright PhD Presidential Scholarship administered by American Indonesian Exchange Foundation (AMINEF) and the Institute for International Education (IIE). In addition, this study is partially funded by grants from NASA's Ocean Surface Topography Science Team project (Univ. of Colorado, 154-5322), NASA's Geodetic Imaging project (NNX12AQ07G), NASA's Application Science Program under the SERVIR project (NNX12AM85G), and The Ohio State University's Climate, Water, and Carbon (http://cwc.osu.edu/) program. i Abstract Fresh water resources are critical for daily human consumption. Therefore, a continuous monitoring effort over their quantity and quality is instrumental. One important model for water quantity monitoring is the rainfall-runoff model, which represents the response of a watershed to the variability of precipitation, thus estimating the discharge of a channel (Bedient and Huber, 2002, Beven, 2012). Remote sensing and satellite geodetic observations are capable to provide critical hydrological parameters, which can be used to support hydrologic modeling. For the case of satellite radar altimetry, limited temporal resolutions (e.g., satellite revisit period) prohibit the use of this method for a short (<weekly) interval monitoring of water level or discharge. On the other hand, the current satellite radar altimeter footprints limit the water level measurement for rivers wider than 1 km (Birkett, 1998, Birkett et al., 2002). Some studies indeed reported successful retrieval of water level for small-size rivers as narrow as 80 m (Kuo and Kao, 2011, Michailovsky et al., 2012); however, the processing of current satellite altimetry signals for small water bodies to retrieve accurate water levels, remains challenging. To address this scientific challenge, this study poses two main objectives: (1) to monitor small (40–200 m width) and medium-sized (200–800 m width) rivers and lakes using satellite altimetry through identification and choice of the over-water radar waveforms corresponding to the appropriately waveform-retracked water level; and (2) to develop a rainfall-runoff hydrological model to represent the response of mesoscale watershed to the variability of precipitation. Both studies address the humid tropics of Southeast Asia, specifically in Indonesia, where similar studies do not yet exist. This study uses the Level 2 radar altimeter measurements generated by European Space Agency’s (ESA’s) Envisat (Environmental Satellite) mission. The first study proves that satellite altimetry provides a good alternative or the only means in some regions to measure the water level of medium-sized river (200–800 m width) and small lake (extent <1000 km2) in Southeast Asia humid tropic with reasonable accuracy. In addition, the procedure to choose retracked Envisat altimetry water level heights via identification or selection of over water waveform shapes is reliable; therefore this study concluded that the use of waveform shape selection procedure should be a standard measure in determining qualified range measurements especially over small rivers and lakes. This study also found that Ice-1 is not necessarily the best retracker as reported by previous studies, among the four standard waveform retracking algorithms for Envisat altimetry observing hydrologic bodies. The second study modeled the response of the poorly-gauged watershed in the Southeast Asia’s humid tropic through the application of Hydrologic Engineering Center – Hydrologic Modeling System (HEC-HMS). The performance evaluation of HEC-HMS discharge estimation confirms a good match between the simulated discharges with the observed ones. As the result of precipitation data analysis, this study found that Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) is the preferred input forcing for the model, given the thorough evaluation of its relationship with field-measured precipitation data prior to its use as primary climatic forcing. This ii research also proposes a novel approach to process the TRMM precipitation estimation spatially through Thiessen polygon and area average hybrid method, which model the spatial distribution of TRMM data to match the spatial location of field meteorological stations. Through a simultaneous validation that compares the water level anomaly transformed from HEC-HMS simulated discharge and satellite altimetry measurement, this study found that satellite altimetry measures water level anomaly closer to the true water level anomaly than the water level anomaly converted from HEC-HMS simulated discharge. Some critical recommendations for future studies include the use of waveform shape selection procedure in the satellite altimetry based water level measurement of small and medium-sized rivers and small lakes, as well as the exploration to implement data assimilation between satellite altimetry and the hydrologic model for better discharge and water level estimations. iii Table of Contents Preface.................................................................................................................................. i Abstract ............................................................................................................................... ii Table of Contents ............................................................................................................... iv 1. Introduction .................................................................................................................... 1 1.1. Fresh Water Resources ............................................................................................ 1 1.2. Hydrology of the Humid Tropics ............................................................................ 3 1.3. Satellite Radar Altimetry......................................................................................... 4 1.4. Motivation and Contribution of this Study ............................................................. 9 2. Theoretical Background ............................................................................................... 11 2.1. Satellite Radar Altimetry....................................................................................... 11 2.1.1. Historical Review........................................................................................ 11 2.1.2. Satellite Altimetry Measurement ................................................................ 12 2.1.3. Error Corrections ........................................................................................ 14 2.1.4. Waveform Retracking ................................................................................. 17 2.1.5. Non-Ocean Surface Waveform Retrackers ................................................. 23 2.2. Hydrological Analysis and Modeling ................................................................... 30 2.2.1. Hydrological Cycle and Watershed Concepts ............................................ 30 2.2.2. Rainfall-runoff Process ............................................................................... 31 2.2.3. Runoff Volume Estimation ......................................................................... 33 2.2.4. Unit Hydrograph ......................................................................................... 38 2.2.5. Flow Routing .............................................................................................. 40 2.2.6. Watershed Hydrologic Modeling ................................................................ 42 3. Satellite Radar Altimetry for Small Water Bodies in the Tropics ................................ 44 3.1. Introduction ........................................................................................................... 44 3.1.1. Monitoring Rivers and Lakes in Humid Tropics ........................................ 44 3.1.2. Remote Sensing and Satellite Altimetry ..................................................... 44 3.1.3. Satellite Altimetry Waveform Retracking Algorithms for Inland Waters .. 44 3.1.4. Motivation and Contribution of This Study ................................................ 44 3.2. Study Area ............................................................................................................. 45 3.2.1. Mahakam River and Lakes in East Kalimantan .......................................... 45 3.2.2. Lake