Terrestrial Water Storage from GRACE and Satellite...
Transcript of Terrestrial Water Storage from GRACE and Satellite...
Terrestrial Water Storage from GRACE and Satellite Altimetry in the Okavango Delta (Botswana)
The HYDRO-GRAV projectOle B. Andersen, P. E. Krogh (DNSC/DTU, Denmark)
P. Bauer-Gottwein, S. Leiriao (DTU, Environment and Ressources) R. Smith, P. Berry, J. Freeman (De Montford, UK)
F. Lemoine (NASA/GSFC, USA)
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Overview
• The Hydrograv Project
• Preliminary results from The Okavango Delta (Botswana)
• NASA/GSFC GRACE Mascon• CNES / BGI Global Spherical harmonic solutions• EAPRS retracked ERS-2/Envisat satellite altimetry• Local river gauge observations.• Hydrological models
– Annual signal – Importance of 3D gravity modelling
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HYDROGRAV
Improving Calibration and Reliability of Large-Scale Hydrological Models with Ground-Based and Space-Borne Time-lapse Gravity Surveys (HYDROGRAV)
Objectives of HYDROGRAV – To understand in detail the relationship between hydrological and
gravity signals over a range of spatial and temporal scales. – To demonstrate the utility of gravity surveys for hydrological
analysis in two target regions in Denmark and Africa. – Improving the GRACE data using groundbased information.– Constrain hydrological parameters using GRACE data
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HYDROGRAV
DTU Danish National Space Center.
DTU Institute of Environment and ressources
COWI – Int. Engineering, environmental science
DHI Water and Ressources
Consortium
Funding Danish Agency for Science, Technology and Innovation3.5 mill kroner = 500.000 Euro
DTU Co-sponsoring two Ph.d students (Pl. see their Poster).
Period
Testregions
2007 – 2010 (3.5 years)
Okavango Delta - Botswana (In situ + Grace) Denmark (pump test)
WWW.HYDROGRAV.DK
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The HYDROGRAV Approach
Numerical hydrological modelImprove parameter estimates
(i.e. Okavango)
Water storage changes Simulated gravity changes
Hydro observationsIn-Situ gravity observationsGrace Gravity Observations
Hydro-Geophysical inverse problem
Hydrological data Conceptual hydro model
Parameter estimates
Geophysical forward problem
TimesteppingHydro model
Hydrology - Gravityinverse constrainGRACE solution
Okavango Gravity survey 2008-2010CG5 Temporal and spatial survey
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Testregions: Okavango , Botswana
Size of Denmark, Essential to a prospority of wildlifeSeasonal Flooding, Water evaporates
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Okavango Delta
Δ S can be obtained from hydrological model (MODFLOW)Δ S can be obtained from GRACE
Δ SSW can be obtained from Retracked altimetry / river gauge
Subsurface water storage: Δ SSM + Δ SGW = ΔS - Δ SSW
ΔS = P – E - RΔS = Δ SSW + Δ SSM + Δ SGW
Hydrological Balance
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Retracking AltimetryEAPRS retracking system
EAPRS expert system identifies eleven waveform shapes and applies tailored retracking algorithm to obtain heights.
EAPRS system was used to analyze ERS-1/2 & ENIVSAT waveform shapes over inland water.
Difficult regions.Retracking varies with timeMost places river dries out.
High slope
Slope
Water
Land/water
Complex
Very wide
SeaIce-Like
Near specular
PatchOcean
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Retracked by R. Smith, EAPRS
Retracked Altimetry10 Years of ERS-2
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ENVISAT
Altimetry range generally larger than model
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NASA/GSFC GRACE MASCONS• Processed GRACE level 1B Data from Jan 2003 – July 2007• Upgraded atmospheric series, improved ocean tide models, improved processing. • Mascons solved on a 4ºx4º grid every ten days, where sufficient data were
available to construct a solution.• GRACE signature from a mascon only manifest itself over the area of overflight.• => 150 10-day solutions (≈ 5 years)
=> Okavango within one MASCON
GRACE
BGI / CNES global GRACE constrained solutions• 5 years of GRACE Level 2 spherical harmonic solutions• Spherical harmonic degree and order 50. • Temporal resolution = 10 days.• 156 10-day solutions ( ≈ 5 years)• Interpolated spatial resolution = 1 degree
0 10 20 30 40 50-40
-30
-20
-10
0
Latit
ude
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GRACE Mascon + Hydrology + Altimetry
GRACE (blue)
GLDAS(green)
ENVISAT(cyan)
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Annual Signal - Okavango
Jan03 Jan04 Jan05 Jan06 Jan07-20
0
20
0
400
800GRACE BGIGRACE masconGLDAS
Discharge[m
3s-1]
Gra
vity
sig
nal
[cm
H20
]
90 = 1 april
138 cm H20
Satellite Altimetry
101 = 10-april86 = 26-march112 = 21-april98 = 07-aprilPhase (days)
9.5 cm H207.2 cm H204.4 cm H20Amplitude
Discharge MohemboGLDASGRACE
masconGRACE BGI
Discharge
Estimated annual + bi-annual signal (6 parameter solution). BGI Bi-annual signal is siqnificantMascon Annual signal is significantly larger than BGI (omission ??)All but Discharge shows trend (íncreased ΔS ?)
Computation: Pernille E. Krogh. Se Poster (Tuesday) by Christiansen and Krogh
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Water Storage Change
Using MODFLOW hydrological model of Okavango Delta.Forward gravity response.
Compute accurate forward gravity response to timevarying hydrological changes. ”Terrain” modeling system from geodesy.Forsberg (exact) close, McMillian(intermediate) and Point mass system outside.
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Preliminary 3D modelling of Okavango
MODFLOW hydrological model Gravity change simulation
Computation S. Leireio
GRACE observations
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The HYDROGRAV Project
Investigate Satellite Altimetry and GRACE at regional scales:
The high resolution GRACE MASCONS shows both annual+interannual signal
GRACE MASCON annual is significantly larger than BGI signal
Altimetric river level observations, gauge and GRACE in agreement on phase
Investigate methods for accurate gravity field response to hydrological change
Will carry out comparison between in-situ and satellite based observations
Use full 3D hydrological model DHI MODFLOW river mask system
Outlook / Summary