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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/S0717-65382004000300026 

  Gayana 68(2): 459-465, 2004

SPACE-TIME CHARACTERIZATION OF PUNTA LAVAPIE UPWELLING SYSTEM THROUGH SS NOAA/AVHRR IMAGES
 
 

Pedro Paolini Cuadra1, Fabiola Rodríguez2 & Carlos Gallardo3

1. Centro de Estudios Espaciales, Universidad de Chile. ppaolini@ing.uchile.cl
2. Memorista de Geografía, Universidad de Chile
3. Memorista de Ing. Informática, Universidad Tecnológica Metropolitana


RESUMEN

La zona de Punta Lavapié en la VIII región del Bio-Bio corresponde a un foco de surgencia costera que presenta períodos de alta y baja actividad durante el año. Es de nuestro interés, entonces, generar una caracterización espacio temporal del sistema de surgencia para dicha área, que además posee una importancia económica relevante debido a los volúmenes anuales de pesca. Se cuenta con una serie de imágenes NOAA/AVHRR de TSM de más de tres años (Diciembre de 1998 hasta Diciembre de 2001) para el sector de Punta Lavapié. Algunas imágenes con nubosidad fueron reconstruidas mediante un interpolador de TSM desarrollado en el CEE, hecho que permitió contar con más imágenes en la serie de tiempo. Se obtuvieron imágenes de promedio estacional y campos de vectores de advección superficial a partir del método objetivo MCC.

ABSTRACT

Punta Lavapié, located in the VIII region of Bio-Bio, is a very important coastal upwelling area which presents high and low activity phases during the year. Through remote sensing technology, a spatial and temporal characterization was generated for Punta Lavapié upwelling system, which has, indeed, economic significance due to big fishing volumes in a normal year. A long-term time series of three years (from December 1998 until December 2001) of SST NOAA/AVHRR images was processed for Punta Lavapié. Some SST images with clouds were reconstructed through a digital image interpolator developed by CEE, which allowed to have more images into the time series. Seasonal average images and advective vector fields through the MCC objective method were obtained to summarize the results.


INTRODUCTION

The knowledge of the coastal systems submissive coastal upwellings is of great importance from an ecological and economic sense. Ecological, because it corresponds to the event that triggers the biological productivity, and economic because in the long run it triggers the development of exploitable species. Therefore, the characterization of systems as these conform a base to sustain the optimal advantage of fishing and benthic resources.

In this work a space and temporal description of the upwelling system of the Punta Lavapié is made (72.7-76 west long. and 36-38.5 south lat.), in the eighth administrative region of Chile based on SST images. The upwelling focus of Punta Lavapié is immediately to the south west of the gulf of Arauco, which characterizes being a rich zone in population of pelagics species larvae (Arcos et al., 1987; Djurfeldt, 1989; Castillo et al., 1991; Arcos et al., 1996; Castro et al., 1997). Thus, and due to in systems bay-upwelling located more to the north occurs the phenomenon of upwelling shadow (Castilla et al., 2002), this phenomenon was expected for the gulf of Arauco.

The upwelling of Punta Lavapié presents periods well defined of high and low activity (Grob et al., 2003). As in rest of upwelling systems in Chile, the phase of high activity of this upwelling center is concentrated in the warm and cold-warm transition seasons, between months September and March. Therefore, the phase of low activity appears in warm-cold transition and cold seasons, between months May and July (Grob et al., 2003).

By another side, the circulation in the neighborhood of upwelling focus and in the gulf of Arauco has special importance for the retention processes of fish larvae and the dynamism, in general, of the early states of these species (Parada et al., 2001).

MATERIALS AND METHODS

A series of NOAA/AVHRR images of polar satellites NOAA-14 and NOAA-16 was processed (19hrs GMT, app.). From these SST images ware obtained being applied the algorithm of atmospheric correction Split Window for the south zone of central Chile. The SST images go from December of 1998 to December of 2001, which generates a time series of three years

Later, the clouds and the continent area were removed from the SST images by means masking by supervised classification (Lagos et al., 2002).

Generation of SST Average Images

According to the different conditions during the year, seasonal average images of SST were defined throughout each one of the years into the time series under study. Thus, such as shows figure 1, 12 images that define the space and time synoptic conditions for the upwelling focus of Punta Lavapié and its neighborhood were generated.

Generation of thermal front accumulated frequency images

Under the same seasonal criterion 12 images of accumulated frequency of thermal fronts were generated (Lagos et al., 2002). These images allow to define the edge of the space dominion and the frequency of the occurrence of the upwelling events, as well as to state the presence of upwelling shadow in some sector of the gulf of Arauco.

Generation of Surface Advection Fields

By means of the application of objective method MCC on sequential images of SST superficial advection fields were generated (Lagos et al., 2002). Images in sequence of 24 hours of separation were used.

Nevertheless, and because many sequential images of SST presented cloudiness in sectors of importance for this study, a process of reconstruction through space interpolation was applied on these.

To reach this goal was developed and implemented an application that reconstructs the values of SST on the sectors of the image which had been covered by clouds and later masked with null values. Thus, the area utilized at the time of executing the cross correlation to determinate surface advection is increased, allowing to count on a greater number of valid vectors for its later analysis.

Basically, the method used for the reconstruction of SST images consists of the variografic analysis of the surrounding data to the mask of null values, interpolating by means of an ordinary Kriging this sector. The implementation of the algorithm of images reconstruction was made programming in Matlab.

Figure 1 gives an example of the reconstruction procedure on a portion of SST image. The figure 1A shows the original image of SST that has portions of masked cloudiness. Subsequent to the process of determination of variogram and its corresponding adjustment to an analytical function (linear, spherical, exponential, Gaussian or of power) the interpolation is executed, as shows the figure 1B.


 
Figure 1. Image reconstruction through Kriging interpolation

By this way, reconstructions were performed over the sequential images of SST in the zone of Punta Lavapié only when the magnitude of the cloudiness masks had a neighborhood of temperature values sufficient to carry out the process of variogram calculation. This because the values of the great magnitude cloud neighborhood often are zero, since these reach the edges of the image, resulting from the interpolation artificial decreasing values towards the center of the masked patch.

RESULTS

Figure 2 shows the series of seasonal average images of SST for the study area. From them it is possible to observe the noticeable intra-annual seasonality in each one of the thermal conditions throughout the year. It is in the warm (Summer) and of cold-warm transition (Spring) seasons that the upwelling focus of Punta Lavapié shows the greater annual activity. The warm season is highlighted because the dominion of cold water intrusion is observed with notoriety in the sector.


 
Figure 2. Seasonal average images of SST, from 1999 until 2001 for Punta Lavapié upwelling focus.

During the warm-cold transition (Autumn) and cold (Winter) seasons is observed in the average images of SST that the space dominion of the upwelling decrease remarkably in relation to the periods of greater activity.
On the other hand, from average images of SST was observed a strong diminution of the SST values from 1999 toward 2001, fact that is possible to observe in graph 1. This one three points within the area were taken from upwelling focus of Punta Lavapié: in front of Lebu, Tirúa and Punta Lavapié. In general, the location north-south order defines the thermal order of magnitude for each one of the sampled points from the average images; thus, the center located in front to Tirúa (to the south of Punta Lavapié) had the lowest values of the series, as well as the located one in front of Punta Lavapié had the highest SST values.


 
Graph 1. Thermal changes during studied period on upwelling focus (from SST average images).

From the accumulated frequency of thermal fronts images is concluded that the maximum space dominion of the upwelling is reached during the warm season (summer) and a minimum space dominion during the cold one. The presence of upwelling shadow into the gulf of Arauco is well-known only during the period of maximum activity of the upwelling and is shown from Punta Lavapié until Santa Maria island (to the Punta Lavapié North).

The surface advection fields generated from MCC method applied to sequential images of SST gave as result currents patterns in according to the visual inspection with the same images. Some of surface advection patterns can be observed in figures 3 and 4.


 
Figure 3. Surface advection fields from MCC method for Punta Lavapié (year 2000).

These advection patterns give an instantaneous vision of the magnitude and direction of the displacement of the drawn up water masses through their surface temperature. For the case of the area in study, an interesting advection pattern is shown on the sector of the gulf of Arauco, which shows surface advection fields of counterclockwise rotation with low speeds.


 
Figure 4. Surface advection fields from MCC method for Punta Lavapié (years 1999 and 2000).

 

REFERENCES

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Arcos, D., S. Núñez & A. Acuña. 1996. "Variabilidad de pequeña escala en la zona nerítica del sistema de surgencia de Talcahuano (Chile central): identificación y dinámica de áreas de retención larval". Gayana Oceanol., 4(1):21-58.         [ Links ] [2]

Castilla J. C., N. Lagos, R. Guiñez & J. Largier. 2002. "Embayments and nearshore retention of plankton: the antofagasta bay and other examples". The Oceanography and Ecology of the Nearshore and bays in Chile. Ediciones Universidad Católica de Chile, Santiago, Chile, 179-203.         [ Links ] [3]

Castillo, G., H. Muñoz, H. González & P. Bernal. 1991. "Daily analysis of abundance and size variability of fish larvae in relation to oceanic water intrusions in coastal areas". Biol. Pesq., 20:21-35.         [ Links ] [4]

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Djurfeldt, L. 1989. "Circulation and mixing in the coastal upwelling embayment, Gulf of Arauco, Chile". Shelf Res., 9: 1003-1016.         [ Links ] [6]

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Parada C., M. A. Sobarzo, D. Figueroa & L. Castro. 2001. "Circulación del Golfo de Arauco en un período de transición estacional: Un nuevo enfoque". Invest. Mar., Valparaíso, 29(1):11-23.         [ Links ] [9]

 

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