New Zealand Journal of Marine and Freshwater Research abstracts

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A method for estimating inherent optical properties of New Zealand continental shelf waters from satellite ocean colour measurements

Matthew H. Pinkerton¹
Gerald F. Moore²
Samantha J. Lavender³
Mark P. Gall⁴
Kadija Oubelkheir⁵
Kenneth M. Richardson¹
Philip W. Boyd⁶
James Aiken²

¹National Institute of Water and Atmospheric Research Limited
Private Bag 14901, Kilbirnie
Wellington, New Zealand
email: m.pinkerton@niwa.co.nz
²Plymouth Marine Laboratory
Prospect Place
Plymouth, United Kingdom
³School of Earth, Ocean and Environmental Sciences (SEOES)
University of Plymouth
Plymouth, United Kingdom
⁴National Institute of Water and Atmospheric Research Limited
P.O. Box 8602
Christchurch, New Zealand
⁵Inland and Coastal Water Remote Sensing
Environmental Remote Sensing Group
CSIRO Land & Water
GPO Box 1666, Canberra
ACT 2601 Australia
⁶National Institute of Water and Atmospheric Research Limited
Centre for Chemical and Physical Oceanography
Department of Chemistry
University of Otago
Dunedin, New Zealand

Abstract We describe a method to estimate spectral absorption and backscattering coefficients between 412 and 555 nm from measurements of remote sensing reflectance across the visible spectrum. The algorithm described is applicable to ocean colour satellite measurements (e.g., SeaWiFS). In situ measurements of inherent and apparent optical properties were made at 19 coastal stations off the north coast of New Zealand’s South Island in December 2001. These measurements were used to parameterise a bio-optical model that estimates remote sensing reflectance from concentrations of water constituents. The model generated a large number (5000) of modelled ocean colour reflectance spectra that represented a greater range of biogeochemical conditions than were measured in the study area. These modelled values spanned a wide range of chlorophyll concentrations (0.1–10 mg m–3), total suspended particulate material concentrations (0.1–50 g m–3), and dissolved yellow substance absorptions (0.01–3 m–1). The modelled spectra were then used to test the performance of the algorithm. The median ratio of algorithm values to target values was 0.84 (absorption), and 0.80 (backscatter), and the median absolute errors were 33% (absorption) and 36% (backscatter) across two orders of magnitude. The r2 values between target and algorithm values of inherent optical properties in log-log space were 0.89 for backscatter, and varied with wavelength for absorption from 0.79 (412 nm), 0.72 (443 nm), 0.63 (490 nm), 0.55 (510 nm), and 0.21 (555 nm).

Keywords SeaWiFS; MODIS; ocean colour; remote sensing; bio-optical algorithm; New Zealand; case 2

New Zealand Journal of Marine and Freshwater Research, 2006, Vol. 40: 227–247
0028–8330/06/4002–0227     © The Royal Society of New Zealand 2006
M05028; Online publication date 10 April 2006. Received 19 May 2005; accepted 21 November 2005

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