Underway spectrophotometry along the Atlantic Meridional Transect reveals high performance in satellite chlorophyll retrievals

REMOTE SENSING OF ENVIRONMENT

卷:183

Article

Brewin, Robert J. W.^1,2  Dall'Olmo, Giorgio^1,2  Pardo, Silvia¹  van Dongen-Vogels, Virginie³  Boss, Emmanuel S.⁴ 

[1] Plymouth Marine Lab, Prospect Pl, Plymouth PL1 3DH, Devon, England

[2] Plymouth Marine Lab, Natl Ctr Earth Observat, Plymouth PL1 3DH, Devon, England

[3] Univ Technol Sydney, Plant Funct Biol & Climate Change Cluster, Sydney, NSW, Australia

[4] Univ Maine, Sch Marine Sci, Orono, ME 04469 USA

关键词: Phytoplanlcton;    Ocean colour;    Remote sensing;    Chlorophyll;    Validation;    Atlantic Ocean;   

DOI  :  10.1016/j.rse.2016.05.005

来源: Elsevier

【 摘 要 】

To evaluate the performance of ocean-colour retrievals of total chlorophyll-a concentration requires direct comparison with concomitant and co-located in situ data. For global comparisons, these in situ match-ups should be ideally representative of the distribution of total chlorophyll-a concentration in the global ocean. The oligotrophic gyres constitute the majority of oceanic water, yet are under-sampled due to their inaccessibility and under-represented in global in situ databases. The Atlantic Meridional Transect (AMT) is one of only a few programmes that consistently sample oligotrophic waters. In this paper, we used a spectrophotometer on two AMT cruises (AMT19 and AMT22) to continuously measure absorption by particles in the water of the ship's flow-through system. From these optical data continuous total chlorophyll-a concentrations were estimated with high precision and accuracy along each cruise and used to evaluate the performance of ocean-colour algorithms. We conducted the evaluation using level 3 binned ocean-colour products, and used the high spatial and temporal resolution of the underway system to maximise the number of match-ups on each cruise. Statistical comparisons show a significant improvement in the performance of satellite chlorophyll algorithms over previous studies, with root mean square errors on average less than half (similar to 0.16 in logio space) that reported previously using global datasets (similar to 0.34 in logio space). This improved performance is likely due to the use of continuous absorption based chlorophyll estimates, that are highly accurate, sample spatial scales more comparable with satellite pixels, and minimise human errors. Previous comparisons might have reported higher errors due to regional biases in datasets and methodological inconsistencies between investigators. Furthermore, our comparison showed an underestimate in satellite chlorophyll at low concentrations in 2012 (AMT22), likely due to a small bias in satellite remote-sensing reflectance data. Our results highlight the benefits of using underway spectrophotometric systems for evaluating satellite ocean-colour data and underline the importance of maintaining in situ observatories that sample the oligotrophic gyres. (C) 2016 The Authors. Published by Elsevier Inc.

【 授权许可】

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