s99u1le2 - Ocean Color Ocean Color Lesson II: Data...

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Project Oceanography Spring Series 1999 -Ocean Color 15 Ocean Color Ocean Color Lesson II: Data Processing and Imagery Ocean color observations made from an Earth orbit allow an oceanographic viewpoint that is impossible from ship or shore -- a global picture of biological activity in the world's oceans. In this lesson we will discuss how the data collected by the satellite sensor are processed to obtain useful products for researchers. Ocean Color Viewed from Space: What Does the Satellite See? The satellite radiometer “sees” light entering the sensor. In the case of ocean color measurements, the satellite is viewing some portion of the earth’s surface and measuring the amount and color (wavelength) of sunlight reflected from the earth’s surface. As ocean color intensity is related to the amount of each of the constituents in seawater, data from the satellite sensor may therefore be used to calculate the concentrations of particulate and dissolved materials in surface ocean waters. The sensor has the capability of making measurements at several visible and infra-red (IR) wavelengths, corresponding to different bands of electromagnetic energy. These are called the spectral bands of the sensor. The earliest ocean color sensor had 6 bands, SeaWiFS (Sea-viewing Wide Field-of-view Sensor) has 8 bands, or channels. Future sensors are planned with many more spectral bands, which will allow scientists to determine more seawater constituents and to do so more accurately. What data do the satellite collect? Data received from an ocean color satellite like the Sea- viewing Wide Field-of view Sensor (SeaWiFS), a global ocean color mission launched in August 1997, is stored and transmitted in
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Project Oceanography Spring Series 1999 -Ocean Color 16 Ocean Color several forms. Global Area Coverage (GAC) data are stored in the satellite's computers and transmitted to receiving stations on earth during the period the satellite is in the dark. (Remember that passive data can only be collected during daylight because sunlight is required for measurements.) Local Area Coverage (LAC) data are transmitted in real-time (as soon as it is collected) to other receiving stations on land where it is stored in land-based computers. Scientists who routinely work with the SeaWiFS data have real-time High Resolution Picture Transmission (HRPT) receivers to collect this LAC data and use it in their research. One other difference between GAC and LAC data is that they are at different resolutions. Each data point is taken in a particular area of the ocean. This area is called a pixel. LAC data pixels cover an area which is 1 km by 1 km in size. GAC data pixels are larger, and cover an area of 4 km by 4 km. Actual pixel sizes differ slightly, because the earth’s surface is curved, and because the satellite is sometimes looking down at the earth at an angle. We say that LAC data have higher resolution than GAC data. However, GAC data have lower
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This note was uploaded on 07/31/2011 for the course OCB 6050 taught by Professor Staff during the Spring '11 term at University of South Florida - Tampa.

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s99u1le2 - Ocean Color Ocean Color Lesson II: Data...

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