TY - JOUR
T1 - Exploitation of error correlation in a large analysis validation: GlobCurrent case study
A1 - Danielson,Richard E.
A1 - Johannessen,Johnny A.
A1 - Quartly,Graham D.
A1 - Rio,Marie-Helene
A1 - Chapron,Bertrand
A1 - Collard,Fabrice
A1 - Donlon,Craig
AD - Nansen Environm & Remote Sensing Ctr, Bergen, Norway.
AD - Plymouth Marine Lab, Plymouth, Devon, England.
AD - Collecte Localisat Satellites, Ramonville St Agne, France.
AD - IFREMER, Plouzane, France.
AD - OceanDataLab, Locmaria Plouzane, France.
AD - European Space Agcy, Noordwijk, Netherlands.
UR - https://doi.org/10.1016/j.rse.2018.07.016
DO - 10.1016/j.rse.2018.07.016
KW - Measurement model
KW - Ocean current
KW - Collocation
KW - Validation
N2 - An assessment of variance in ocean current signal and noise shared by in situ observations (drifters) and a large gridded analysis (GlobCurrent) is sought as a function of day of the year for 1993-2015 and across a broad spectrum of current speed. Regardless of the division of collocations, it is difficult to claim that any synoptic assessment can be based on independent observations. Instead, a measurement model that departs from ordinary linear regression by accommodating error correlation is proposed. The interpretation of independence is explored by applying Fuller's (1987) concept of equation and measurement error to a division of error into shared (correlated) and unshared (uncorrelated) components, respectively. The resulting division of variance in the new model favours noise. Ocean current shared (equation) error is of comparable magnitude to unshared (measurement) error and the latter is, for GlobCurrent and drifters respectively, comparable to ordinary and reverse linear regression. Although signal variance appears to be small, its utility as a measure of agreement between two variates is highlighted. Sparse collocations that sample a dense (high resolution) grid permit a first order autoregressive form of measurement model to be considered, including parameterizations of analysis-in situ error cross-correlation and analysis temporal error autocorrelation. The former (cross-correlation) is an equation error term that accommodates error shared by both GlobCurrent and drifters. The latter (autocorrelation) facilitates an identification and retrieval of all model parameters. Solutions are sought using a prescribed calibration between GlobCurrent and drifters (by variance matching). Because the true current variance of GlobCurrent and drifters is small, signal to noise ratio is near zero at best. This is particularly evident for moderate current speed and for the meridional current component
Y1 - 2018/11
PB - Elsevier Science Inc
JF - Remote Sensing Of Environment
SN - 0034-4257
VL - 217
SP - 476
EP - 490
ID - 57713
ER -