The Satellite and The Instrument

 

The SAC-C is the first operational argentinean satellite for Earth observation and it has among it´s payloads a camera (named MMRS, Multispectral Medium Resolution Scanner) specially designed for terrestrial and marine ecosystems studies.

The spectral bands of the camera were selected to satisfy the use requirements in land, coastal water and interior water.

Actually the SAC-C is in a quasi-polar sun-syncronous orbit at an altitude of 705 km. It is part of the Morning Constellation jointly with the NASA satellites Landsat 7, Terra and EO-1. The local time of the descending node pass is 10:21 +/- 6 minutes.

The MMRS is a "push-broom" sensor with the following characteristics:

 

Spatial

 

1.     Pixel Size: 175 m.

 

2.     Observed Swath: 360 km,  a bit more than 2000 pixels in the image.

 

3.     Observed Area Height: it depend on the capture start and end times, whose in turn depends on the acquisition mode, how is detailed as following:

 

§        Real Time Acquisitions : The number of lines depends on the time that the satellite is on the field of view of the ground segment, normally is greater than 30000 which implies captures with a height of more than 5000 km.

 

§        Storage Mode Acquisitions: The solid state recorder memory allows to store approximately 9000 lines, which implies captures with a height of more than 1500 km.

 

Temporal

 

Revisit time of 9/7 days, when the satellite is in the constellation.

 

Spectral

 

Band 1:    480 – 500   nm     greenish blue

Band 2:    540 – 560   nm     green

Band 3:    630 – 690   nm     red

Band 4:    795 – 835   nm     near IR (NIR)

Band 5:  1550 – 1700 nm     short wave IR (SWIR)

 

Radiometric

 

The values specified by design of the sensor saturation for each band are detailed in the following table. Those values could change slowly with time due to degradation of sensor elements caused by the exposition to radiation.

 

The maximum radiance is quantified with an 8 bits dynamic range which implies that it has 256 levels or digital counts.

 

Band

Lmax

[mW/(sr.cm2)]

1

0,317

2

0,6164

3

1,4076

4

0,8972

5

0,48