数据说明
VIIRS Chlorophyll a (chlor_a)
上传时间：2019-05-22 23:43:49 浏览次数：作者与来源：admin
Chlorophyll a refers to the amount of chlorophyll a in a unit volume of seawater.
Unit: mg/m3
Resolution: 9km pixel, daily, monthly
Duration: Jan. 2012 to on-going.
Source: Visible infrared Imaging Radiometer(VIIRS), NASA
Version: 2018
Processing: Original daily and monthly mean products are shown.
The chlorophyll-a here is calculated using an empirical relationship derived from in situ measurements of chlor_a and remote sensing reflectances (Rrs) in the blue-to-green region of the visible spectrum.
The chlor_a product combines two algorithms, the O'Reilly band ratio OC3V algorithm and the Hu color index (CI) algorithm (chl_hu).
The CI algorithm is a three-band reflectance difference algorithm employing the difference between Rrs in the green band and a reference formed linearly between Rrs in the blue and red bands.
CI = Rrs(λgreen)-[ Rrs(λblue)+ (λgreen – λblue)/( λred – λblue)*( Rrs(λred)- Rrs(λblue))]
where λblue = 443nm, λgreen = 551nm, and λred = 671nm.
The OC3V algorithm is a fourth-order polynomial relationship between a ratio of Rrs and chlor_a.
where the numerator, Rrs(λblue) = Rrs(443), the denominator, Rrs(λgreen) = Rrs(551) the coefficients, a0= 0.2228, a1=-2.4683, a2= 1.5867, a3= -0.4275, a4=-0.7768.
The coefficients were derived using version 2 of the NASA bio-Optical Marine Algorithm Data set (NOMAD).
For chlorophyll retrievals below 0.15 mg m-3, the CI algorithm is used.
For chlorophyll retrievals above 0.2 mg m-3, the OC3V algorithm is used.
In between these values, the CI and OC3V algorithm are blended using a weighted approach.
Known issues
1. This refinement is restricted to relatively clear water, and the general impact is to reduce artifacts and biases in clear-water chlorophyll retrievals due to residual glint, stray light, atmospheric correction errors, and white or spectrally-linear bias errors in Rrs. As implemented, the algorithm diverges slightly from what was published in Hu et al. (2012) in that the transition between CI and OC3V now occurs at 0.15 < CI < 0.2 mg/m3 to ensure a smooth transition.
2. A limited set of satellite-to-in-situ match-up validation results are available for VIIRS from the validation tool of the SeaWiFS Bio-Optical Archive and Storage System (SeaBASS). And the result shows a mean bias of 1.04269 and a mean absolute error(MAE) of 1.48207.
Reference
Hu, Chuanmin, Zhongping Lee, and Bryan Franz. Chlorophyll a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference. Journal of Geophysical Research, 2012,117(C1). DOI: 10.1029/2011jc007395
O'Reilly, J.E., Maritorena, S.,Mitchell, B. G., Siegel, D. A., Carder, K. L., Garver, S. A., Kahru, M., & McClain, C. R.. Ocean color chlorophyll algorithms for SeaWiFS, Journal of Geophysical Research, 1998,103(C11), 24937-24953. DOI: 10.1029/98JC02160.
O'Reilly, J.E., & 24 co-authors. SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3. NASA Tech. Memo. 2000-206892, Vol. 11, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 2000,49 pp.
All the contents of this page are quoted from NASA. All project documentation and related publications can be found at the website:https://oceancolor.gsfc.nasa.gov/
Unit: mg/m3
Resolution: 9km pixel, daily, monthly
Duration: Jan. 2012 to on-going.
Source: Visible infrared Imaging Radiometer(VIIRS), NASA
Version: 2018
Processing: Original daily and monthly mean products are shown.
The chlorophyll-a here is calculated using an empirical relationship derived from in situ measurements of chlor_a and remote sensing reflectances (Rrs) in the blue-to-green region of the visible spectrum.
The chlor_a product combines two algorithms, the O'Reilly band ratio OC3V algorithm and the Hu color index (CI) algorithm (chl_hu).
The CI algorithm is a three-band reflectance difference algorithm employing the difference between Rrs in the green band and a reference formed linearly between Rrs in the blue and red bands.
CI = Rrs(λgreen)-[ Rrs(λblue)+ (λgreen – λblue)/( λred – λblue)*( Rrs(λred)- Rrs(λblue))]
where λblue = 443nm, λgreen = 551nm, and λred = 671nm.
The OC3V algorithm is a fourth-order polynomial relationship between a ratio of Rrs and chlor_a.
where the numerator, Rrs(λblue) = Rrs(443), the denominator, Rrs(λgreen) = Rrs(551) the coefficients, a0= 0.2228, a1=-2.4683, a2= 1.5867, a3= -0.4275, a4=-0.7768.
The coefficients were derived using version 2 of the NASA bio-Optical Marine Algorithm Data set (NOMAD).
For chlorophyll retrievals below 0.15 mg m-3, the CI algorithm is used.
For chlorophyll retrievals above 0.2 mg m-3, the OC3V algorithm is used.
In between these values, the CI and OC3V algorithm are blended using a weighted approach.
Known issues
1. This refinement is restricted to relatively clear water, and the general impact is to reduce artifacts and biases in clear-water chlorophyll retrievals due to residual glint, stray light, atmospheric correction errors, and white or spectrally-linear bias errors in Rrs. As implemented, the algorithm diverges slightly from what was published in Hu et al. (2012) in that the transition between CI and OC3V now occurs at 0.15 < CI < 0.2 mg/m3 to ensure a smooth transition.
2. A limited set of satellite-to-in-situ match-up validation results are available for VIIRS from the validation tool of the SeaWiFS Bio-Optical Archive and Storage System (SeaBASS). And the result shows a mean bias of 1.04269 and a mean absolute error(MAE) of 1.48207.
Reference
Hu, Chuanmin, Zhongping Lee, and Bryan Franz. Chlorophyll a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference. Journal of Geophysical Research, 2012,117(C1). DOI: 10.1029/2011jc007395
O'Reilly, J.E., Maritorena, S.,Mitchell, B. G., Siegel, D. A., Carder, K. L., Garver, S. A., Kahru, M., & McClain, C. R.. Ocean color chlorophyll algorithms for SeaWiFS, Journal of Geophysical Research, 1998,103(C11), 24937-24953. DOI: 10.1029/98JC02160.
O'Reilly, J.E., & 24 co-authors. SeaWiFS Postlaunch Calibration and Validation Analyses, Part 3. NASA Tech. Memo. 2000-206892, Vol. 11, S.B. Hooker and E.R. Firestone, Eds., NASA Goddard Space Flight Center, 2000,49 pp.
All the contents of this page are quoted from NASA. All project documentation and related publications can be found at the website:https://oceancolor.gsfc.nasa.gov/
