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2012 AGU Chapman Conference on Remote Sensing of the ...

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snow transiti<strong>on</strong> <strong>of</strong> individual storms has a str<strong>on</strong>g influence<strong>on</strong> <strong>the</strong> difference between snowdepth in <strong>the</strong> open and underforest canopy.Kosuth, PascalA method for river discharge estimate from satelliteobservati<strong>on</strong> al<strong>on</strong>e, without any in situmeasurementKosuth, Pascal 1 ; Négrel, Jean 1 ; Strauss, Olivier 2 ; Baume, Jean-Pierre 3 ; Faure, Jean-Baptiste 4 ; Litrico, Xavier 3, 5 ; Malaterre,Pierre-Olivier 31. TETIS, IRSTEA, M<strong>on</strong>tpellier, France2. LIRMM, Université M<strong>on</strong>tpellier 2, M<strong>on</strong>tpellier, France3. GEAU, IRSTEA, M<strong>on</strong>tpellier, France4. Hydrologie-Hydraulique, IRSTEA, Ly<strong>on</strong>, France5. LyRE, R&D Center, Ly<strong>on</strong>naise des Eaux, Bordeaux,FranceIs it possible to estimate river discharge from satellitemeasurement <strong>of</strong> river surface variables (width L, water levelZ, surface slope Is, surface velocity Vs) without any in situmeasurement ? Current or planned satellite observati<strong>on</strong>techniques in <strong>the</strong> hydrology-hydraulic domain are limited to<strong>the</strong> measurement <strong>of</strong> surface variables such as river width L(optical and SAR imagery), water level Z (radar and Lidaraltimetry), river surface l<strong>on</strong>gitudinal slope Is (cross-trackinterferometry) and surface velocity Vs (al<strong>on</strong>g-trackinterferometry). On <strong>the</strong> opposite, river bottom parameterssuch as river bottom height (Zb), river bottom l<strong>on</strong>gitudinalslope (Ib), Manning coefficient (n), vertical velocity pr<strong>of</strong>ilecoefficient ( <strong>the</strong> ratio between mean water velocity andsurface velocity), that are key data for discharge estimate andmodeling, cannot be measured by satellite. They require insitu measurement (Zb, Ib, ) and model calibrati<strong>on</strong> (n). Wepresent here a method to derive river bottom parametersfrom satellite measured river surface variables in <strong>the</strong> absence<strong>of</strong> any in situ measurement. This will <strong>the</strong>n allow us toestimate river discharge for any set <strong>of</strong> surface variables. Themethod relies <strong>on</strong> a set <strong>of</strong> hydraulic hypo<strong>the</strong>sis (for instancerectangular secti<strong>on</strong>, c<strong>on</strong>stant Manning coefficient n andc<strong>on</strong>stant velocity pr<strong>of</strong>ile coefficient ). It c<strong>on</strong>sists <strong>of</strong> solvingan equality c<strong>on</strong>straint between two formulati<strong>on</strong>s linking <strong>the</strong>river discharge Q to <strong>the</strong> surface variables and <strong>the</strong> unknownparameters (Q1 and Q2 obtained from <strong>the</strong> massc<strong>on</strong>servati<strong>on</strong> equati<strong>on</strong> and <strong>the</strong> energy c<strong>on</strong>servati<strong>on</strong>equati<strong>on</strong>): Q1=L..Vs.h Q2=L.h 5/3 .Is 1/2 .[n 2 +g -1 .h 1/3 .(Is-Ib)]where h=Z-Zb Given a river secti<strong>on</strong>, estimating <strong>the</strong> riverbottom parameters (, Zb, Ib, K) is achieved by using a set <strong>of</strong>surface variables (L, Z, Is, Vs) i=1 to N, measured <strong>on</strong> this secti<strong>on</strong>at various times ti throughout <strong>the</strong> hydrological cycle, and bydetermining <strong>the</strong> set <strong>of</strong> river bottom parameters thatminimizes a deviati<strong>on</strong> criteria between (Q1)i and (Q2)i. Thisminimizati<strong>on</strong> is achieved by iterative or direct methods,depending <strong>on</strong> <strong>the</strong> type <strong>of</strong> criteria and <strong>on</strong> additi<strong>on</strong>alhypo<strong>the</strong>sis (ex. a uniform regime hypo<strong>the</strong>sis leads to ananalytical soluti<strong>on</strong>). Several simulati<strong>on</strong>s have shown <strong>the</strong>efficiency <strong>of</strong> <strong>the</strong>ses methods <strong>on</strong> exact simulated data set (i.e.for which (Q1)i=(Q2)i). We have assessed <strong>the</strong> robustness <strong>of</strong><strong>the</strong>se methods to measurement noise <strong>on</strong> river surfacevariables. We proposed several modificati<strong>on</strong>s to increase thisrobustness and <strong>the</strong> ability to provide acceptable riverdischarge estimates (error

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