Satellite Environmental Monitoring of Oil Spills in the South Gulf Of Mexico
Authors: Mendoza Arturo , Miranda Fernando P. , Bannerman Karen , Pedroso Enrico , López Oscar , Herrera Miguel 
Published: October 2008

PEMEX Exploration and Production have been using a progressive application of RADARSAT-1 satellite in Campeche Bay for offshore oil slick detection with ancillary and meteo oceanographic calibration since 2000.

A multiyear monitoring program has been in progress combining successfully its results with oil spill modelers and GIS for complementary support in environmental issues.

Introduction

An oil seep report from a fisherman was the origin of Cantarell, the biggest Mexican oil field located on the Campeche Bay, in the Southern Gulf of Mexico. Nowadays, PEMEX Exploration and Production (PEP) share their operational marine area with a high activity of natural oil seeps (Figure 1), as well as with important vessel traffic related to fisheries or industrial transport.

Nevertheless, any oil record on the sea or on the beaches of this area is immediately related to PEP activities or facilities generating claims and social pressures with economic and public image impacts.

After the Ixtoc-1 oil spill on 1979, PEMEX focused its attention to enhance its environmental resources. In order to improve monitoring and evaluation capabilities, since 1999 PEMEX has begun to use Geographical Information Systems and remote sensing for oil slick detection and analysis. This work describes our four year experience with the RADARSAT-1 satellite applications, and how it has developed and integrated as a complementary tool for an operational monitoring multiyear program.

SAR theory for oil slick detection

Satellite marine application is a progressive technology that allows improving spatial and temporal coverage with a lower cost in relation to traditional monitoring (i.e. oceanographic or aerial surveys). Nevertheless, as any other new technology it is necessary to verify its use under different conditions to define limits and strengths. Scientific papers could be an option to the academy, but not good enough for operational requiriments. Offshore activities from PEP required a remote sensing tool with oil detection capability, accuracy results and time delivery opportunity.

Synthetic Aperture Radar (SAR) sensors generate and receive microwave between 3 to 23.5 cm wavelengths (Raney, 1998). Unlike optical sensors, microwave energy penetrates clouds, rain, smoke, dust, or haze thus enabling SAR systems to collect data under any atmospheric condition.

The physical mechanism that allows detection of oil seeps and spills is the dampening of capillary waves present on the ocean surface. These capillary waves, which are only a few centimeters in length, produce backscattering of the incident radar pulse due to a Bragg scattering mechanism (Johannessen et al., 1994). As a result, ocean regions containing oil are dark in contrast with the background radar signal (clutter).

Critical meteo-oceanographic conditions for oil slick detection are winds and waves high. The range of wind velocity considered ideal for oil detection using SAR lies between 3 to 10 m.s-1 and represent a user limitation (Staples and Hodgins, 1998). In addition, sea state conditions suitable for oil seep detection are characterized by wave heights of less than 1.5m.