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ASA_WV__0P: ASAR Wave Mode Level 0
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6.6.8 Doppler Centroid parameters

The Doppler centroid of the image is estimated once for stand-alone products , and is hence reported once. For stripline , however, a Doppler centroid estimate is performed at least at the start and at the end of a slice . To ensure the user is given a
complete record of the Doppler parameters used during processing, the Doppler Centroid Coefficients ADS is updated with a new ADSR at every granule for stripline processing. Each update is time stamped with the zero Doppler time to which the update applies. The Doppler centroid coefficients used on range lines between two updates are found by linear interpolation between the updated and previous values. The contents of each update (each update is a single ADSR within the ADS) are as shown in the table below:

Table 6.44 Doppler Centroid parameters

Doppler Centroid parameters

# Description Units Count Type Size
Data Record
0 zero_doppler_time
Zero Doppler azimuth time at which estimate applies
MJD 1 mjd 12 byte(s)
1 attach_flag
Attachment Flag

Always set to zero for this ADSR

flag 1 BooleanFlag 1 byte(s)
2 slant_range_time
2-way slant range time origin (t0)
ns 1 fl 4 byte(s)
3 dop_coef
Doppler centroid coefficients as a function of slant range time: D0, D1, D2, D3, and D4.

Where Doppler Centroid = D0 + D1(tSR-t0) + D2(tSR-t0)2 + D3(tSR-t0)3 + D4(tSR-t0)4

HzHz/sHz/s2Hz/s3Hz/s4 5 fl 5*4 byte(s)
4 dop_conf
Doppler Centroid Confidence Measure.

Value between 0 and 1, 0 = poorest confidence, 1= highest confidence

- 1 fl 4 byte(s)
5 dop_conf_below_thresh_flag
Doppler Centroid Confidence below threshold flag.

0=confidence above threshold, centroid calculated from data; 1=confidence below threshold, centroid calculated from orbit parameters

flag 1 BooleanFlag 1 byte(s)
6 delta_dopp_coeff
Delta Doppler coefficents DelatD0(SS1) , DelatD0(SS2) DelatD0(SS3) DelatD0(SS4) DelatD0(SS5)
- 5 ss 5*2 byte(s)
7 spare_1
- 1 SpareField 3 byte(s)
Record Length : 55

DS_NAME : Doppler Centroid parameters

Format Version 114.0  

Note: For Field# 5:

Doppler Centroid Confidence Measure:

Value between 0 and 1, 0 = poorest confidence, 1= highest confidence

If multiple Doppler Centroid estimates were performed, this value is the lowest confidence value attained.

Doppler Confidence Below Threshold Flag

0 = confidence above threshold, Doppler Centroid calculated from data

1 = confidence below threshold, Doppler Centroid calculated from orbit parameters

For a discussion of the Doppler Centroid estimation algorithms, refer to the included technote " Doppler Centroid Frequency Estimator " . See also " Level 1B Essential Product Confidence Data " in chapter 2.