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Operational Modes

The main mode of operation of RA2 is the TRACKING mode. During this mode all instrument's units are powered-on and operative. The main task is the tracking of echo waveform which is executed without interruption. 

The second mode of operation is the IF CALIBRATION mode.

One of the components of the Envisat RA-2 sensor is an Intermediate Frequency (IF) Pass Band Filter. In theory, the spectrum of the impulse response of such a filter should be a rectangle, but in reality this is not the case.

In order to compensate for the distortion on the RA-2 waveforms due to this component, the measurement of the filter impulse response is needed.

To retrieve the shape of the IF Filter impulse response spectrum, the RA-2 is commanded to operate in the so-called IF Calibration mode. This consists of the measurement of noise power spectra by setting the instrument in listen-only mode (no power transmitted) and putting the receiving window delay to a value such that no echo from the surface could be received.

The different IF Calibration strategies applied during the whole Envisat mission are summarized in the table here below. In the table detailed IF masks acquisition for both ascending (A) and descending (D) overpasses over Himalaya and Rocky Mountains.

 

Cycle

Date

Himalaya

Rocky Mountains

From beginning of mission to cycle 30

Up to 04 Oct 2004

A

-

From cycle 31 to 52 

From

4 Oct 2004 to

13 Nov 2006

A   D

-

53

13 Nov 2006

A   D

The CTI_IFC table with

Rx_Distance = 90 microsecond;

start orbit #24604 at ANX=0.

-

54

18 Dec 2006

A   D

CTI_IFC table with

Rx_Distance = 100 microsecond;

start orbit #25105 at ANX=0

-

55

22 Jan 2007

A   D

CTI_IFC table with

Rx_Distance = 81 microsecond;

start orbit #25606 at ANX=0.

-

From cycle 56 to 61

From

26 Feb 2007 to

24 Sep 2007

A

A   D

From cycle 62 to 64

24 Sep 2007

A

A   D

New procedure for IF calibration (through Digital BITE Mode command)

65

07 Jan 2008

A   D

New procedure for IF calibration (through Digital BITE Mode command) only over descending passes

-

From cycle 66 to end of mission

11 Feb 2008

A

New procedure for IF calibration (through Digital BITE Mode command)

-