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CZCS-derived pigment concentration fields in Japanese coastal area
Adv. Space Res. Vol. 7, No. 2, pp. (2)79—(2)82, 1987 Printed in Great Britain. All rights reserved.
0273—1177/87 80.00 + .50 Copyright © COSPAR
CZCS-DERIVED PIGMENT CONCENTRATION FIELDS IN JAPANESE COASTAL AREA H. Fukushima,* K. Hiramatsu** andY. Sugimori* * Faculty of Marine Science and Technology, Tokai University, Orido, Shimizu, 424 Japan * *Far Seas Fisheries Research Laboratory, Japan Fisheries Agency, Orido, Shimizu, 424 Japan
ABSTRACT
About ten CZCS scenes were atmospherically corrected to investigate chlorophyll—like pigment concentration levels around Japan.* Three of the images were compared to ship—sampled data which were obtained within 5 days from satellite overpasses, showing fairly good agreement with the pigment range of 0.1 to 5,ug/1. Highly reflective patterns were observed in a late spring scene, suspected to be due to abundance of coccolithophorids which are algae with calcium carbonate shell. Some problems in processing CZCS data in Japanese area are also discussed. CHLOROPHYLL IMAGES NOAA—supplied CZCS data tapes were processed using “Gordon—Clark” atmospheric correction algorithm /1/ implemented on a Z—8000 micro—processor based UNIX system. In—water algorithm /2/ that relates water—leaving radiances to chlorophyll concentration were applied to the corrected data to get pigment concentration images. The Kuroshio, a western boundary current at Pacific Ocean, streams along southeastern coast of Japan, and leaves off the coast eastward near Cape Inubo. Photo. 1 clearly shows the contrast between the coastal water and the Kuroshio water in terms of pigment concentration. The area near Cape Inubo is associated with high chlorophyll concentration probably because of nutrient—rich land discharge and, in fact, good fishing ground are for~~iedthroughout the year. Although the water mass south to the Kuroshio main stream is generalized as oligotrophic water, there is variety in the concentration with some turbulent features including cyclonic eddy (A in Photo.1). To the north of the Kuroshio meander, the picture indicates cyclonic and anticyclonic eddies (B) together with phytoplankton patches along the coastline (C). The northeastern area between the Kuroshio Extension and the cold Oyashio Front is geographically referred to as the Tohoku Area. In addition to these two regimes, a warm Tsugaru Current flows in the area from Tsugaru Strait, making the area highly perturbed. Photo. 2 clearly depicts the features of the area: Phytoplankton—rich Oyashio intrusions into the warm water (A’s in photo.), anticyclonic eddies including a warm core ring with diameter of about 100km (B) and the coastal waters with high pigment concentration which are entrained into the warm core ring or into the Tsugaru Current (C). Chlorophyll concentration level around Japan in this season stays generally low. But, with enough nutrient supply, the northern part of the area is characterized with its high chlorophyll concentration throughout the year, providing important fishing ground. & summer image obtained on July 29, 1981, (not shown) shows low pigment concentration around Japan except some very near coastal waters, supporting results of pigment level observation conducted routinely by JMA (Japan Meteological Agency) research vessels.
While most images seem to give consistent results with the ship—measured pigment observations, some atmospherically corrected images have negative L~(water—leavingradiance) at 443nn band which is probably due tc the error in evaluating molecular—scattered sun light in the atmosphere.
*
In this paper, “chlorophyll—like pigment” means chlorophyll—a and phaeophytin—a pigments. (2)79
H. Fukushima, K. Hiramatsu and Y. Sugimori
(2)80
~
:~~.ii
Photo. 1
CZCS—derived pigment image (Apr.
~
14, 1981).
____
IA
_____
—A
~
i~ 2 Photo.
______
A
____
_
~.
I.~PuurTr~ -~1981). CZCS—derived pigment image (Sept. 17,
KAIDO)
A PAN
.6.
Photo. 3
Atmospherically corrected image of 520 nm band data (June 5, 1980) with (520,670)=1.0.
Pigment Concentration Fields
(2)81
~::101 April 29, 1980
:~i:
1
31°~O’
(a) Along 135
10
April 28, 1981
1 141°
142°
32°30’
32°
33°
33°30’
K line (Süiith of Honshu).
0
143°
144°
145°
146°
147°
148°
(b) Along 41’ 30’ N line (South of Hokkaido).
101 July 29, 1981 ~1O0;5
—2
10 135’36’
136°
136°30’
137°
137~3O’
138°
13830’
(c) Along the Japan Sea lines.
Fig. 1
Comparisons between ship-measured (solid points) and CZCS-estimated (solid line) surface pigment concetrations. Attached figure with each point indicates number of days past the satellite overpass.
(2)82
H. Fukushima, K. Hiramatsu and Y. Sugimon PATTERNS WITH HIGH REFLECTIVITY
Photo. 3 shows atmospherically corrected image at 520nm band for the Tohoku Area in June, 1980. White patterns observed are highly reflective at the 443, 520 and 550nm bands relative to surrounding water, this feature is clearly distinguished from clouds because of relatively low reflectivity in 670mm. The Possibility of influence from terrestrial suspended matter is dismissed since the area is distant from the coast and the sea is deep. Thus, these patterns are suspected to be due to coccolithophorids, as those reported in /3/. COMPARISONS WITH SHIP—SAMPLED MEASUREMENTS CZCS—derived pigment concentrations in three images were compared to JMA ship—sampled data sets /4/, which were obtained within 5 days from satellite overpasses. In Fig. 1 (a), satellite—derived concentrations were calculated from LW(520)/Lw(550), since corrected LW(443) can be negative, causing discrepancies from the sea—truth. Fig. 1 (b) shows fairly good agreement except for high pigment concentration cases. This disagreement might be explained by the difference in sampling method or by limitation of the estimation algorithm. The comparison in Fig. 1 (c), which has relatively low pigment range, also shows good agreement except for the data with very low concentration. To summarize, the satellite—derived estimates seemed to be in good agreement with the sea—truth which has the pigment range of 0.1 to 5~g/l, although some deviation may arise for other cases. CONCLUSION Since CZCS images give chlorophyll maps that interpret ship observational data well, the authors consider that, to a certain extent, the Gordon—Clark approach is workable for the data around Japan. But for more precise estimation, the following aspects should be noted. (1) As pointed out in /5/, “clear water area” that serve as an anchor point for the atmospheric correction, is not necessarily present in every scene. (2) There are high sediment loadings in the East China Sea and the Yellow Sea, where the Gordon—Clark scheme will not be applicable. The in—water algorithm might also be different. (3) Aerosol types may be different in the Pacific side and the Japan Sea side. As an example, the effect of “Yellow Sand” transported by winds from the main land China, which is often observed in March—May, might be considered. (4) Estimated water—leaving radiance at 443mm often becomes negative, suggesting the necessity of more accurate evaluation of Rayleigh scattering path iadiance in the atmosphere. Although ocean color remote sensing has not yet become popular in Japan, fishermen are starting to have a keen interest in such data, hoping to utilize ocean color data as new fisheries information in addition to satellite—derived sea surface temperature maps currently issued by the Japan Fisheries Information Center /6/. A 5—year research project sponsored by Japan Fisheries Agency was started in 1985 to investigate and/or develop algorithms including atmospheric correction that are efficient and suitable for Satellite data in Japanese area. REFERENCES 1. 2.
3.
4. 5. 6.
P.M. Zion, Description of algorithm for Processing Coastal Zone Color Scanner (CZCS) Data, JPL Publication, 83—98 (1983). H.R. Gordon, D.K. Clark, J.W. Brown, O.B. Brown, R.H. Evans, and W.W. Broenkow, Phytoplankton pigment concentration in the middle Atlantic Bight: comparison of ship determinations and CZCS estimates, Applied Optics, 22, #1, 20 (1983). P.M. Holligan, M. Viollier, D.S. Harbour, P. Camus, and N. Champagne—Philippe, Satellite and ship studies of coccolithophore production along a continental shelf edge, Nature, 304, #28, 339 (1983). The Japan Meteorological Agency, The results of marine meteorological and oceanographical observations, 67, 69 and 70. T. Ogishima, H. Fukushima, and Y. Sugimori, Problems relating to atmospheric correction algorithm for CZCS data in Japanese coastal area (in Japanese), Bull. Airborne and Satellite Phys. & Fish. Oceanogr. #8, 53 (1986) H. Tameishi and I. Yamanaka, Application of NOAA AVHRR data for fisheries service, Proc. Int. Sym. Ocean Space Utilization, Springer—Verlag (1985).
0273—1177/87 80.00 + .50 Copyright © COSPAR
CZCS-DERIVED PIGMENT CONCENTRATION FIELDS IN JAPANESE COASTAL AREA H. Fukushima,* K. Hiramatsu** andY. Sugimori* * Faculty of Marine Science and Technology, Tokai University, Orido, Shimizu, 424 Japan * *Far Seas Fisheries Research Laboratory, Japan Fisheries Agency, Orido, Shimizu, 424 Japan
ABSTRACT
About ten CZCS scenes were atmospherically corrected to investigate chlorophyll—like pigment concentration levels around Japan.* Three of the images were compared to ship—sampled data which were obtained within 5 days from satellite overpasses, showing fairly good agreement with the pigment range of 0.1 to 5,ug/1. Highly reflective patterns were observed in a late spring scene, suspected to be due to abundance of coccolithophorids which are algae with calcium carbonate shell. Some problems in processing CZCS data in Japanese area are also discussed. CHLOROPHYLL IMAGES NOAA—supplied CZCS data tapes were processed using “Gordon—Clark” atmospheric correction algorithm /1/ implemented on a Z—8000 micro—processor based UNIX system. In—water algorithm /2/ that relates water—leaving radiances to chlorophyll concentration were applied to the corrected data to get pigment concentration images. The Kuroshio, a western boundary current at Pacific Ocean, streams along southeastern coast of Japan, and leaves off the coast eastward near Cape Inubo. Photo. 1 clearly shows the contrast between the coastal water and the Kuroshio water in terms of pigment concentration. The area near Cape Inubo is associated with high chlorophyll concentration probably because of nutrient—rich land discharge and, in fact, good fishing ground are for~~iedthroughout the year. Although the water mass south to the Kuroshio main stream is generalized as oligotrophic water, there is variety in the concentration with some turbulent features including cyclonic eddy (A in Photo.1). To the north of the Kuroshio meander, the picture indicates cyclonic and anticyclonic eddies (B) together with phytoplankton patches along the coastline (C). The northeastern area between the Kuroshio Extension and the cold Oyashio Front is geographically referred to as the Tohoku Area. In addition to these two regimes, a warm Tsugaru Current flows in the area from Tsugaru Strait, making the area highly perturbed. Photo. 2 clearly depicts the features of the area: Phytoplankton—rich Oyashio intrusions into the warm water (A’s in photo.), anticyclonic eddies including a warm core ring with diameter of about 100km (B) and the coastal waters with high pigment concentration which are entrained into the warm core ring or into the Tsugaru Current (C). Chlorophyll concentration level around Japan in this season stays generally low. But, with enough nutrient supply, the northern part of the area is characterized with its high chlorophyll concentration throughout the year, providing important fishing ground. & summer image obtained on July 29, 1981, (not shown) shows low pigment concentration around Japan except some very near coastal waters, supporting results of pigment level observation conducted routinely by JMA (Japan Meteological Agency) research vessels.
While most images seem to give consistent results with the ship—measured pigment observations, some atmospherically corrected images have negative L~(water—leavingradiance) at 443nn band which is probably due tc the error in evaluating molecular—scattered sun light in the atmosphere.
*
In this paper, “chlorophyll—like pigment” means chlorophyll—a and phaeophytin—a pigments. (2)79
H. Fukushima, K. Hiramatsu and Y. Sugimori
(2)80
~
:~~.ii
Photo. 1
CZCS—derived pigment image (Apr.
~
14, 1981).
____
IA
_____
—A
~
i~ 2 Photo.
______
A
____
_
~.
I.~PuurTr~ -~1981). CZCS—derived pigment image (Sept. 17,
KAIDO)
A PAN
.6.
Photo. 3
Atmospherically corrected image of 520 nm band data (June 5, 1980) with (520,670)=1.0.
Pigment Concentration Fields
(2)81
~::101 April 29, 1980
:~i:
1
31°~O’
(a) Along 135
10
April 28, 1981
1 141°
142°
32°30’
32°
33°
33°30’
K line (Süiith of Honshu).
0
143°
144°
145°
146°
147°
148°
(b) Along 41’ 30’ N line (South of Hokkaido).
101 July 29, 1981 ~1O0;5
—2
10 135’36’
136°
136°30’
137°
137~3O’
138°
13830’
(c) Along the Japan Sea lines.
Fig. 1
Comparisons between ship-measured (solid points) and CZCS-estimated (solid line) surface pigment concetrations. Attached figure with each point indicates number of days past the satellite overpass.
(2)82
H. Fukushima, K. Hiramatsu and Y. Sugimon PATTERNS WITH HIGH REFLECTIVITY
Photo. 3 shows atmospherically corrected image at 520nm band for the Tohoku Area in June, 1980. White patterns observed are highly reflective at the 443, 520 and 550nm bands relative to surrounding water, this feature is clearly distinguished from clouds because of relatively low reflectivity in 670mm. The Possibility of influence from terrestrial suspended matter is dismissed since the area is distant from the coast and the sea is deep. Thus, these patterns are suspected to be due to coccolithophorids, as those reported in /3/. COMPARISONS WITH SHIP—SAMPLED MEASUREMENTS CZCS—derived pigment concentrations in three images were compared to JMA ship—sampled data sets /4/, which were obtained within 5 days from satellite overpasses. In Fig. 1 (a), satellite—derived concentrations were calculated from LW(520)/Lw(550), since corrected LW(443) can be negative, causing discrepancies from the sea—truth. Fig. 1 (b) shows fairly good agreement except for high pigment concentration cases. This disagreement might be explained by the difference in sampling method or by limitation of the estimation algorithm. The comparison in Fig. 1 (c), which has relatively low pigment range, also shows good agreement except for the data with very low concentration. To summarize, the satellite—derived estimates seemed to be in good agreement with the sea—truth which has the pigment range of 0.1 to 5~g/l, although some deviation may arise for other cases. CONCLUSION Since CZCS images give chlorophyll maps that interpret ship observational data well, the authors consider that, to a certain extent, the Gordon—Clark approach is workable for the data around Japan. But for more precise estimation, the following aspects should be noted. (1) As pointed out in /5/, “clear water area” that serve as an anchor point for the atmospheric correction, is not necessarily present in every scene. (2) There are high sediment loadings in the East China Sea and the Yellow Sea, where the Gordon—Clark scheme will not be applicable. The in—water algorithm might also be different. (3) Aerosol types may be different in the Pacific side and the Japan Sea side. As an example, the effect of “Yellow Sand” transported by winds from the main land China, which is often observed in March—May, might be considered. (4) Estimated water—leaving radiance at 443mm often becomes negative, suggesting the necessity of more accurate evaluation of Rayleigh scattering path iadiance in the atmosphere. Although ocean color remote sensing has not yet become popular in Japan, fishermen are starting to have a keen interest in such data, hoping to utilize ocean color data as new fisheries information in addition to satellite—derived sea surface temperature maps currently issued by the Japan Fisheries Information Center /6/. A 5—year research project sponsored by Japan Fisheries Agency was started in 1985 to investigate and/or develop algorithms including atmospheric correction that are efficient and suitable for Satellite data in Japanese area. REFERENCES 1. 2.
3.
4. 5. 6.
P.M. Zion, Description of algorithm for Processing Coastal Zone Color Scanner (CZCS) Data, JPL Publication, 83—98 (1983). H.R. Gordon, D.K. Clark, J.W. Brown, O.B. Brown, R.H. Evans, and W.W. Broenkow, Phytoplankton pigment concentration in the middle Atlantic Bight: comparison of ship determinations and CZCS estimates, Applied Optics, 22, #1, 20 (1983). P.M. Holligan, M. Viollier, D.S. Harbour, P. Camus, and N. Champagne—Philippe, Satellite and ship studies of coccolithophore production along a continental shelf edge, Nature, 304, #28, 339 (1983). The Japan Meteorological Agency, The results of marine meteorological and oceanographical observations, 67, 69 and 70. T. Ogishima, H. Fukushima, and Y. Sugimori, Problems relating to atmospheric correction algorithm for CZCS data in Japanese coastal area (in Japanese), Bull. Airborne and Satellite Phys. & Fish. Oceanogr. #8, 53 (1986) H. Tameishi and I. Yamanaka, Application of NOAA AVHRR data for fisheries service, Proc. Int. Sym. Ocean Space Utilization, Springer—Verlag (1985).