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[1] The primary goal of the Ice, Cloud and land Elevation Satellite (ICESat) mission is ice sheet elevation change detection. Confirmation that ICESat is achieving its stated scientific requirement of detecting spatially-averaged changes as small as 1.5 cm/year requires continual assessment of ICESat-derived elevations throughout the mission. We use a GPS-derived digital elevation model (DEM) of the salar de Uyuni, Bolivia for this purpose. Using all twelve ICESat passes over the salar survey area acquired to date, we show that the accuracy of ICESat-derived elevations is impacted by environmental effects (e.g., forward scattering and surface reflectance) and instrument effects (e.g., pointing biases, detector saturation, and variations in transmitted laser energy). We estimate that under optimal conditions at the salar de Uyuni, ICESatderived elevations have an absolute accuracy of <2 cm and precision of <3 cm. Citation:

[1] Seasonal variability in ocean bottom pressure p b is analyzed using GRACE (Gravity Recovery and Climate Experiment) data products and an optimized model solution obtained by fitting most available ocean data in a leastsquares sense. The annual cycle in the spatial mean is a substantial part of the observed seasonal p b variability; net freshwater input and atmospheric pressure effects are both important. For the residual spatially-varying patterns, GRACE and model results agree well over the Southern Ocean where strongest variability at both annual and semiannual periods is present. Phase patterns tend to match well, although model amplitudes are generally weaker. Considerable uncertainty remains in both GRACE and model p b fields, judging from the spread among available estimates. Improving the p b estimates requires removal of data noise from aliasing and leakage of land hydrology signals, and further optimization of the ocean model, including possible use of GRACE data to constrain the solution. Citation: Ponte, R. M., K. J. Quinn, C. Wunsch, and P. Heimbach (2007), A comparison of model and GRACE estimates of the large-scale seasonal cycle in ocean bottom pressure, Geophys. Res. Lett., 34, L09603,

[1] Knowledge of the relationship between bottom pressure p b and sea level z is important for understanding ocean circulation and climate. We use recent Gravity Recovery and Climate Experiment (GRACE) Release-05 data along with altimetry to investigate the relationship between z and p b over long periods (>1 year) and large scales (>750 km). Elevated p b signals are observed over deep extratropical regions (e.g., Southern Ocean basins) and shallow or semi-enclosed areas (e.g., Indonesian and Nordic seas). In these places, considerable z variance is explained by p b variance. Correlation between z and p b is significant in many regions, including instances of significant negative correlation suggestive of active baroclinic processes. Results exemplify the good quality of GRACE Release-05 data and demonstrate that contemporary regional z variability cannot always be interpreted in terms of steric changes alone. Citation: Piecuch, C. G., K. J. Quinn, and R. M. Ponte (2013), Satellite-derived interannual ocean bottom pressure variability and its relation to sea level, Geophys. Res. Lett., 40,[3106][3107][3108][3109][3110]

[1] Previous theoretical and model-based studies of the relationship between ocean bottom pressure ( p b ) and sea level (z) suggest primarily barotropic variability at mid to high latitudes for scales greater than a few hundred kilometers and periods less than a few months. We use 7-day GRACE solutions and equivalent satellite altimetry maps, spatially smoothed over 750 km, to investigate the relation between p b and z. The observed fields are significantly coherent at high latitudes for periods of 14-180 days and mid latitudes for periods of 30-100 days. The admittance amplitude between observed p b and z is close to 1 for higher frequencies and drops off for lower frequencies. The results provide, for the first time, global observational evidence for the barotropic nature of largescale ocean variability at mid and high latitudes. We also demonstrate that GRACE data contain significant information over the oceans at periods <60 days, i.e., shorter than the nominal monthly time resolution. Citation: Quinn, K. J., and R. M. Ponte (2012), High frequency barotropic ocean variability observed by GRACE and satellite altimetry, Geophys. Res. Lett., 39, L07603,