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Gayana (Concepción)

versión impresa ISSN 0717-652Xversión On-line ISSN 0717-6538

Gayana (Concepc.) v.68 n.2 supl.TIIProc Concepción  2004

http://dx.doi.org/10.4067/S0717-65382004000300024 

  Gayana 68(2): 450-455, 2004

MULTISPECTRAL TRACKING OF PHYTOPLANKTON IN THE COLOMBIAN CARIBBEAN
 
 

V. V. Ojeda Caicedo1 & A. Plata Gómez2

1. Faculty of Basic Sciences, Technological University of Bolivar, Group of Investigation in Environmental Systems, Cartagena, Colombia, Km1 Via Turbaco; E-mail:vojeda@unitecnologica.edu.co
2. Department of Physics, Industrial University of Santander, Group of Optics and Signal processing, Bucaramanga, Colombia; E-mail:aplata@uis.edu.co


ABSTRACT

In a quantitative research study, the concentration and circulation of group of micro-organisms "phytoplankton" have been found trough the images of the ocean colour in the Colombian Caribbean Sea. These images have been observed trough the Sea Star satellite. The method logical procedure was to collect a number of ocean images at the 1A level of the sensor SeaWifs. This only covered the geographical area of study and the seasons of the year. The selection criterion was to give priority to the absence of clouds in the area. Afterwards, the images were analyzed to create mosaics in convenient periods of the to, in turn visualize the periodical changes of the micro-organisms. Thus place with higher concentration of phytoplankton in the study site were identified. This led to quantitative analyses of the concentration level of the subject of study. To analyze the images analytic algorithms were used to fit the sensor. The atmospheric correction of the SeaWifs images was made with the SeaDas software to obtain levels two and three of the images. This was done to calculate the primary production of phytoplankton.

Words Keys: ocean color, primary production, SeaWifs, SeaDas.


INTRODUCTION

One of the basic problems of oceanography has to do with the synoptic and continuous examination of the properties of an oceanic region. In the sea these properties can be studied in detail in a small area around a boat. But, at the same time, it is not possible to compare the properties of the region with critic conditions that are happening simultaneously at a distance of 5 or 100 km of distance. The sensors flying in satellites have extended the study area and have provided the ability to repeatedly observe great regions of the ocean.

Nevertheless, because the collection of data is necessarily limited to the electromagnetic radiation, the obtainable oceanographic information is directly restricted to the superficial layers of the ocean (the Violette, 1974). Even though better sensors will be developed in the future, these will always have limitation. This is because 90% of the ascending visible lights emerging from the water column towards the atmosphere originate in the first optical depth. At this depth the descendent irradiance attenuates 37% when it penetrates the water. If we considered that the bottom of the eufótica zone is the depth where the light attenuates 1% of the superficial value, the eufótica zone has 4,6 optical depths. Therefore, remote sensors data provides averaged information (22%) of the optical components and of the optical properties of the ocean water in the eufotica zone (Kirk, 1994).

It is possible to calculate the new production of the oceans using different models from images of pigments. The new production represents the critical component that limits the transportation of CO2, from the surface to the deep waters. It also represents the maximum limit of biomass to removed from an ecosystem without collapsing it. This tool opens a new possibility for the study the flows of carbon in the regional and global scales. Producing information on the organic productivity from the images of remote spectroradiometer is also useful for a better handling of oceanic fishing. It can also help understand better the impact of natural phenomena that can be catastrophic, for example, the event ENSO (Niño-Oscillation's of the South).

At present, a specialized set of tools is dedicated to the service of research in order to processing of images it exists to the service of the investigation, everything a specialized set of tools that helps to make the image processing. These tools can be used to predict and to characterize the sets of existing systems in the sea and its movements, using satellite images. This alternative has been little developed in the Caribbean region and many other region of South America.

The fundamental support of this investigation is the study of the movements and the concentration displayed by the set of micro organism's phytoplankton in the Colombian Caribbean Sea. All this is based on a frequency range that can radiate when it is affected by the rays of sun. For many regions of the world the colour of the ocean is determined primarily, by the abundance of Phytoplankton and its pigments of photosynthesis associate. The satellite images show the concentrations of Phytoplankton in blue and green, where as the concentration of pigments of Phytoplankton increases it produces a change of blue from blue to green.

Plankton plays a significant role in the exchange process of vitally important gases that takes place between the ocean and the atmosphere.

Besides allowing research related to oceanography, the satellite images allow us to experiment in other field like, pollution control, for example, gases and particles suspended in the atmosphere can be observed with the possibility of determining the precedence or origin, devices and mechanisms of dispersion of the atmospheric pollution. As far as oceanography it is possible to determine, heat concentrations, amount of suspended dead particles in the surface of the ocean, among others. Also the wave of outer flows of radiation at the level of the atmosphere that determines the variation of the Earth climate can be determined.

METHODOLOGY

In this work, the analysis consisted of making a selection of color images of the ocean in level 1A of the SeaWifs sensor, that covered the studied area (chlorophyll: 6,53-20,55N with 68,46-80,83W) and that corresponded to the same time of the year. The selection criterion was to prioritize the cloud absence in the zone; then msl12 and bl2map were reprocessed by means of the algorithms to perform atmospheric corrections and to make projection of map of the respective images (Figure 1. Corrected image) to carry out mosaics in periods of advisable time to visualize the periodic change of the set of micro organisms phytoplankton. All this in order to identify spots from the studied zone with greater concentration of phytoplankton. It was then possible to carry out statistical report.


 
Figure 1. Corrected Multiespectral image for Chlorophyll_a

DATA

In order to make the analysis of the pursuit of biological processes in marine areas of the Colombian Caribbean, the variables of colour of the ocean were obtained by the SeaWifs sensor (Sea-viewing sensorial faithful Wide of view). This description is for the period 1997-1998 and 2000-2003 for chlorophyll a and atmospherics parameters.

The data of chlorophyll are obtained from data of the colour of the ocean registered by the SeaWifs sensor located in the satellite of polar orbit SeaStar to 705 km of the Earth. This sensor allows obtaining data of chlorophyll in oceanic waters of the first optical depth (between 1 and 10 ms), using level 2 (data GAC derived from geophysical parameters) and band 4 of the signal of the sensor (510 nm absorption band of chlorophyll).

In order to obtain the images, the atmospheric characteristics and to download the information it was necessary to request access authorization. It was kindly granted by the subdivision The Ocean Colour Data Support Team of the NASA, thanks to the type of work that was being developed.

The images were processed in the free software of the NASA, the SeaDas that runs under Linux platform, with the purpose of reading and manipulating the information of the data base.

Once the images of level 1 were turned into level 2, the values of chlorophyll were found in mg/m3 for the zone of study. The values of chlorophyll were found by means of algorithm OC4 Version 4, which was developed in May of 2000 like modification to algorithm OC2. This bio-optic algorithm, relates radiation bands for chlorophyll to the polynomial equation of order 4:

 

(Ec.1)

Where,

(Ec.2)

RESULTS

Once the methodology described above applied, it was possible to obtain a general description of the biological processes of the Colombian Caribbean.

Initially a comparative analysis of the magnitude of the values averages every month in every year in the period from 1997 to 2003 was carried out. This was done by means of the MATLAB and the SeaDAS (Example: Figure 2 and 3). Of these values averages was concluded that the concentration of clorofila_a, is bigger in January, May, November and December with values total averages of 0,86, 0,78, 0,74 and 0,61 mg/m3 respectively. The monthly values per year were plotted and as example, in the Figure 4, one can possible estimate the variability of the values. Also, the graphs of the averaged monthly values for every year were deviced. We observed certain periodicity of the chlorophyll (Figure5).


 
Figure 2. January Average, 2003 (MATLAB)


 
Figure 3. May Average 1998 ( SeaDas)

The concentration of chlorophyll in the Colombian Caribbean, is relatively homogenous, from Punta Faro in the Atlantic to the Gulf of Uraba, with diminutions in the Guajira coast. It also possible to appreciate enough biological activity between the Gulf of Uraba and Punta Arboletes, the Rosary Islands and Bocas de Ceniza, where the Magdalena River enters ocean. The productivity of phytoplankton may de due to the fact that the river sends great amount of particles in suspension into the sea. The particles are both organics and inorganic. The river also sends into the ocean dissolved nutrients which activate the growth of phytoplankton.


 
Figure 4. Monthly average of the chlorophyll_a for 1998


 
Figure 5. Monthly Average of Chlorophyll in the Colombian Caribbean (Years: 1997, 1998, 2000, 2001, 2002, 2003)

Three representative zones, were identify 1 between Punta Piedra and Punta Gigantón, zone 2 between Punta Canoas and Punta Faro and zone 3 in Punta Espada (Figures 6).


 
Figure 6. Representative points Colombian Caribbean

Once analyzed the temporary variability and its similarity in the different points, by means of the calculation of the averages, these points could be determined by means of the historical series of chlorophyll.

CONCLUSIONS, ACKNOWLEDGMENTS, REFERENCES

5.1. Conclusions

- Chlorophyll tends to present major concentrations near the coastal zone of the Colombian Caribbean.

- It was possible to verify that the biological process of the Colombian Caribbean can be followed from the information of chlorophyll with the points selected in three sectors of the region, due to the fact that the
variations in these points showed a high degree of representation for the whole study zone.

- The monthly chlorophyll values present seasonal variations, since the biological activity is higher in the months of December, January and May according to the obtained values.

- In the averages obtained from the processed images, it is possible to visualize that there is a great productivity of chlorophyll very close to the Colombian Caribbean Coast. This probably happens because of the exchange activity occurring in the area (because the river enters the sea and because of the oceanic dynamic in the coastal area).

- The image selection criterion consisted of giving priority to the absence of clouds in the area. The presence of clouds in very high al different time of the year, due to the area where the study zone is located (Equatorial zone).

 

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