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Ocean Color Inferred from Radiometers on Low-Flying Aircraft

View Article: PubMed Central - PubMed

ABSTRACT

The color of sunlight reflected from the ocean to orbiting visible radiometers has provided a great deal of information about the global ocean, after suitable corrections are made for atmospheric effects. Similar ocean-color measurements can be made from a low-flying aircraft to get higher spatial resolution and to obtain measurements under clouds. A different set of corrections is required in this case, and we describe algorithms to correct for clouds and sea-surface effects. An example is presented and errors in the corrections discussed.

No MeSH data available.


Measured downwelling irradiance E(λ) in W m-2 nm-1 divided by the cosine of the solar zenith angle ϕ. Horizontal line represents the median value of all data. Black data points were rejected for reasons described in the text, so only the red (clear sky) and blue (cloudy sky) data points were used in the averaged spectra. a) λ = 412 nm. b) λ = 443 nm. c) λ = 490 nm. d) λ = 510 nm. e) λ = 555 nm. f) λ = 670 nm. g) λ = 765 nm.
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f3-sensors-08-00860: Measured downwelling irradiance E(λ) in W m-2 nm-1 divided by the cosine of the solar zenith angle ϕ. Horizontal line represents the median value of all data. Black data points were rejected for reasons described in the text, so only the red (clear sky) and blue (cloudy sky) data points were used in the averaged spectra. a) λ = 412 nm. b) λ = 443 nm. c) λ = 490 nm. d) λ = 510 nm. e) λ = 555 nm. f) λ = 670 nm. g) λ = 765 nm.

Mentions: To process the data, we first averaged each sensor output over about 1 second and rejected data where the aircraft was banked and where the illumination was changing rapidly. To implement the first condition, we calculated the change in aircraft direction at each second using the three data points centered on the point of interest. If the change was greater than 0.05 radians, the central point was rejected. This threshold corresponds to a turn rate of 0.05 rad s-1, or a bank angle of about 15° for the nominal flight speed of 50 m s-1. To implement the second condition, we rejected a data point if the change in the irradiance in the center channel (509 nm) was different by more than 10% from the point before or the point after. All values of irradiance satisfying these conditions are plotted in Figure 3.


Ocean Color Inferred from Radiometers on Low-Flying Aircraft
Measured downwelling irradiance E(λ) in W m-2 nm-1 divided by the cosine of the solar zenith angle ϕ. Horizontal line represents the median value of all data. Black data points were rejected for reasons described in the text, so only the red (clear sky) and blue (cloudy sky) data points were used in the averaged spectra. a) λ = 412 nm. b) λ = 443 nm. c) λ = 490 nm. d) λ = 510 nm. e) λ = 555 nm. f) λ = 670 nm. g) λ = 765 nm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3927510&req=5

f3-sensors-08-00860: Measured downwelling irradiance E(λ) in W m-2 nm-1 divided by the cosine of the solar zenith angle ϕ. Horizontal line represents the median value of all data. Black data points were rejected for reasons described in the text, so only the red (clear sky) and blue (cloudy sky) data points were used in the averaged spectra. a) λ = 412 nm. b) λ = 443 nm. c) λ = 490 nm. d) λ = 510 nm. e) λ = 555 nm. f) λ = 670 nm. g) λ = 765 nm.
Mentions: To process the data, we first averaged each sensor output over about 1 second and rejected data where the aircraft was banked and where the illumination was changing rapidly. To implement the first condition, we calculated the change in aircraft direction at each second using the three data points centered on the point of interest. If the change was greater than 0.05 radians, the central point was rejected. This threshold corresponds to a turn rate of 0.05 rad s-1, or a bank angle of about 15° for the nominal flight speed of 50 m s-1. To implement the second condition, we rejected a data point if the change in the irradiance in the center channel (509 nm) was different by more than 10% from the point before or the point after. All values of irradiance satisfying these conditions are plotted in Figure 3.

View Article: PubMed Central - PubMed

ABSTRACT

The color of sunlight reflected from the ocean to orbiting visible radiometers has provided a great deal of information about the global ocean, after suitable corrections are made for atmospheric effects. Similar ocean-color measurements can be made from a low-flying aircraft to get higher spatial resolution and to obtain measurements under clouds. A different set of corrections is required in this case, and we describe algorithms to correct for clouds and sea-surface effects. An example is presented and errors in the corrections discussed.

No MeSH data available.