Science Requirements for Hydrologic Storage Change from the SWOT Mission

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Science Requirements for Hydrologic Storage
Change from the SWOT Mission
Hyongki Lee1, Doug Alsdorf1,2, Michael Durand1,2,
Jianbin Duan1, C.K. Shum1
1School of Earth Sciences, The Ohio State
University 2Byrd Polar Research Center, The Ohio
State University
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Introduction

• Surface Water Ocean Topography Mission (SWOT)
• Regular direct measurement
• of water height and area
• Storage Change Measurement
• ?S(H2-H1)(A1A2)/2 ?HA
• Potentially up to lakes of size 1ha
• with sub-weekly temporal resolution
• Virtual Mission
• Peace Athabasca Delta (PAD), Canada

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Procedure to estimate SWOT storage change error
35-day repeat Envisat measurement
High-frequency component from daily gauge data
Daily hTruth
Add SWOT height error, N(0,sh)
Water Mask
SWOT orbit overlay Spatio-temporal sampling
Alake N(0,sA)
?hSWOT
ASWOT
?SSWOT
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Dataset to Develop Truth
Water Mask from Landsat
Lake Athabasca
Lake Athabasca
10 km
18-Hz Envisat retracked measurement
Credit Tamlin Pavelsky, UCLA
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Creating daily hTruth (Envisat Gauge)
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Create hTruth for unobserved lakes
1) Characterize and quantify the underlying
hydrologic processes
2) Simulate height variations for the unobserved
lakes
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Created True Height Anomaly
Day 1
Day 31
Day 61
Day 91
Day 121
1274 lakes 1ha
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SWOT Orbit Overlay
Day 5
Day 7.5
Day 4.5
Day 2
Day 21
Day 10.5
Day 13.5
Day 18
22-day Repeat Orbit SWATH coverage as shaded
hSWOT hTruth N(0,sh)
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Simulated hSWOT
Measurement errors are scaled with respect to
of pixels in each lake
Worst Case Scenario 50 m by 50 m pixel size 50
cm height accuracy
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Monthly Storage Change from SWOT

• ASWOT ATruth N(0,sA)
• ?SSWOT ?hSWOT ASWOT

Credit Yongwei Sheng, UCLA
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Storage Change Error of SWOT
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Storage Change Error using Different Orbits
Median 9.30
Median 9.45
Median 9.35
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Conclusion and Future Studies

• How small a lake can be observed?
• ? At least lakes of 250 meter by 250 meter
• How accurate the storage change can be
  estimated?
• ? Better than 510 storage change error
• Future study areas
• ? Amazon, Alaskan/Siberian Arctic lakes

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Temporal Sampling Gap
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Relative Storage Change Error
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a72, ß-0.68
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For a 3 ns pulse length, diameter of footprint is
2.4 km
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Lake Athabasca
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0.89/16.47
0.90/13.14
0.93/13.28
ICE-1
0.87/20.93
0.88/19.54
0.84/19.21
SEAICE
0.89/25.64
0.91/22.65
0.86/20.44
ICE-2