Stephen K. Gill

Variation of Great Lakes water levels derived from Geosat altimetry

A technique for using satellite radar altimetry data to estimate the temporal variation of the water level in moderate to large lakes and enclosed seas is described. Great Lakes data from the first 2 years of the U.S. Navys Geosat Exact Repeat Mission (November 1986 to November 1988), for which there is an improved orbit, are used to demonstrate the technique. The Geosat results are compared to the lake level data collected by the Great Lakes Section, National Ocean Service, National Oceanic and Atmospheric Administration, and are found to reproduce the temporal variations of the five major lakes with root-mean-square error (rms) ranging from 9.4 to 13.8 cm and a combined average of 11.1 cm. Geosat data are also analyzed for Lake St. Clair, representing a moderate-sized lake, with a resulting rms of 17.0 cm. During this study period, the water level in the Great Lakes varied in a typical annual cycle of about 0.2 m (0.5 m for Lake Ontario) superimposed on a general decline of approximately 0.5 m. The altimeter data reproduced the general decline reasonably well for all the lakes, but the annual cycle was obscured in some lakes due to systematic errors in the altimeter data. Current and future altimetry missions will have markedly improved accuracy which will permit many moderate (25 km diameter) or larger lakes or enclosed seas to be routinely monitored.

The Harvest Experiment: Monitoring Jason-1 and TOPEX/POSEIDON from a California Offshore Platform Special Issue: Jason-1 Calibration/Validation

We present calibration results from Jason-1 (2001–) and TOPEX/POSEIDON (1992–) overflights of a California offshore oil platform (Harvest). Data from Harvest indicate that current Jason-1 sea-surface height (SSH) measurements are high by 138 ± 18 mm. Excepting the bias, the high accuracy of the Jason-1 measurements is in evidence from the overflights. In orbit for over 10 years, the T/P measurement system is well calibrated, and the SSH bias is statistically indistinguishable from zero. Also reviewed are over 10 years of geodetic results from the Harvest experiment.

Continuous monitoring of the Jason-1 and TOPEX/Poseidon ocean altimetry missions from dedicated calibration sites

We present calibration results from Jason-1 and TOPEX/Poseidon overflights of the three dedicated verification sites: (1) a California offshore oil platform (Harvest); (2) the Mediterranean island of Corsica (Cape Senetosa), and (3) the Bass Strait off the coast of Tasmania. The high-accuracy of the Jason-1 measurement system is evident in the results from the dedicated calibration experiments. These experiments do indicate, however, that the Jason-1 sea-surface-height (SSH) measurements are biased high by approximately 12-15 cm. We discuss the implications of geographically correlated errors on the determination of the SSH bias.

Adaptation and Mitigation

In the ten years since the first National Assessment of the Potential Consequences of Climate Variability and Change, the science and policy landscape for adaptation has evolved significantly. Adaptation is emerging as an essential strategy for managing climate risk and a broad range of adaptation initiatives are being pursued across a range of geopolitical scales. This interest in adaptation has emerged from an increased awareness that climate impacts are unavoidable (Wetherland et al., 2001); a growing availability of knowledge, data, and tools for the assessment of climate risk; and the interest of government agencies, businesses, and communities in increasing their resilience to both current climate variability as well as future climate change. However, adaptation strategies are not generally mainstreamed into the policy apparatus of governments or the development plans of the private sector; in other words, adaptation strategies supplement existing planning efforts but often involve an effort on their own rather than being integrated into existing management and policy regimes. Also, although adaptation planning has an increasingly rich portfolio of case studies contributing to shared learning (Gregg et al., 2011), the implementation of adaptation plans has proceeded at a much slower pace.

UTILIZING TIDAL CONSTITUENT AND RESIDUAL INTERPOLATION TO SIMULATE WATER LEVELS AND DETERMINE PATTERNS OF INUNDATION

At a location where installation of a NOAA tidal station was not possible, Tidal Constituent and Residual Interpolation (TCARI) was used to interpolate water levels between two locations with observed water levels. One year of interpolated water levels was collected and a full suite of tidal analyses were completed based on the interpolated water level data set. These analyses include datums computations, inundation analyses, seasonal analyses, and harmonic analyses. Results indicate that interpolating water levels with TCARI can be a suitable alternative when collecting water levels at a specified location is not possible.

Calibrating the Jason-1 measurement system

We present calibration results from Jason-1 (2002-) and TOPEX/Poseidon (1992-) overflights of dedicated verification sites on the Mediterranean island of Corsica and on a California offshore oil platform (Harvest). Harvest served for a decade (1992-2002) as a calibration site for the TOPEX/Poseidon (T/P) mission, and is serving in a similar capacity for Jason-1. Initiated in 1996, the Corsica experiment features a fiducial reference station near Aspretto, and a primary sub-satellite tide-gauge deployment site 40 km south at Cape Senetosa. Both Corsica and Harvest feature carefully designed collocations of space-geodetic and tide-gauge systems to support the absolute calibration of the altimetric sea-surface height (SSH). By incorporating improved estimates of the Jason-1 sea-state bias and columnar atmospheric wet path delay, we observe a bias of about 12 cm.