SAR Integration

Integration time

SAR operation requires that the target to be acquired is illuminated during an integration time so that the synthetic antenna length is properly created with the distance travelled by the SAR instrument.

In the case of push-broom modes the integration time must be observed at the beginning and end of the image data take as additional lead and trail time margins.

The integration time is based on the Synthetic Aperture Length (LSA) as follows:

LSA = λ × SR / LAT, with (in meters):

• λ being the wavelength

• SR being the slant range

• LAT being the antenna length in the along track direction

For a stripmap collected at 800 km of slant range and for a 9.6 GHz (3 cm wavelength) system with a 3 m antenna along-track:

• LSA = 0.03 × 800,000 / 3 = 8,000 meters

Assuming 7.5 km/sec satellite speed, the integration time required should be

• integration time = 8/ 7.5 = 1.067 seconds

This figure should be split in two parts, a lead time of 1.067 / 2 = 0.53 sec and an equal size trail part.

 

Configuring SAR integration

To configure SAR integration you may use the sensor wizard.

The sensor must be configured as a SAR sensor.

Click on the "SAR integration..." button, to define the SAR antenna length and the SAR signal frequency (from which the wavelength λ is obtained. Make sure the "Enable" check box is checked.

Otherwise you may always edit the sensor from the properties pane and configure and enable SAR integration. It is important that the sensor is of SAR type.

 

Integration time operation

With SAR integration has been configured, each acquisition will show the swath footprint corresponding to the actual imaging strip plus the calculated lead and trail integration times, corresponding actually to one half the actual SAR integration time.

The acquisition duration will be the sum of the 3 items: lead + imaging + trail