Sensors

Introduction

Satelliteborne optical remote sensing of water has until recently been achieved mainly by systems based on multispectral radiometers with a limited number of bands. Examples include the Advanced Very High Resolution Radiometer (AVHRR) series of sensors which have two bands in the visible/near infrared region and three bands in the TIR region and the higher resolution LANDSAT TM and SPOT X series sensors with three or four bands in the visible/near infrared region and, in the case of LANDSAT TM, three additional TIR bands. For ocean colour applications the SeaWiFS (6 visible, 2 near infrared bands, launched in 1997), MODIS- TERRA /AQUA (20 visible/near infrared/short wave infrared and 16 thermal infrared bands , launched in 1999/2002) and MERIS (15 visible/near infrared bands, launched in 2002) sensors have become widely used. Though the latter two claim in their names to be “imaging spectrometers” the spectral resolution remains incomplete when compared to the hundreds of bands measured by other, non-satellite imaging spectrometer systems.

However, in the coming years improvements in the data transfer rate for satellite-ground transmission and in the capacity of mass data storage facilities needed for global satellite missions will facilitate the use of spaceborne imaging spectrometers with much finer spectral resolution, thus providing more information to improve the detection and discrimination of both land and water features. As an example the atmospheric correction of data and subsequent quantification of chlorophyll-a concentration in turbid coastal and inland waters is considered as critically dependent on sufficient spectral information. At present a number of experimental or pre-operational missions such as CHRIS (62 visible and near infrared bands, launched in 2001 on the small pointable PROBA-1 platform), and HYPERION (220 visible, near infrared and short wave infrared bands, launched in 2000) exist and can be considered as forerunners for the next generation of spaceborne imaging spectrometer.

Source: http://www.ioccg.org/sensors_ioccg.html

The choice of the sensors used depends on many factors:

What do I want to investigate?
Do I need a high spectral resolution?
What are the preferred bands?
Do I need a high spatial resolution?

The price of the images will also contribute to the decision. MUMM currently uses images of 4 different satellite sensors:

SeaWiFS, MERIS and MODIS images are retrieved at a regular base and successfully transformed into total suspended matter and chlorophyll maps while CHRIS is still in an experimental phase.

The following figure compares the spectral response function of SeaWiFS, MERIS and MODIS sensors.