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ASA_WV__0P: ASAR Wave Mode Level 0
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ASA_APC_0P: ASAR Alternating Polarization Level 0 (Copolar)
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ASA_IMS_1P: ASAR Image Mode Single Look Complex
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6.6.14 Ocean Wave Spectra

This MDS contains the ocean wave spectrum of the imagette . There is one MDSR per wave cell. The format of the wave-spectrum MDS closely matches that of the cross spectrum MDS where some fields in the cross-spectrum MDS are substituted
by new values pertaining to the ocean wave spectrum product. Each ocean wave spectrum MDSR is described below:


Table 6.51 Ocean Wave Spectra

Ocean Wave Spectra

# Description Units Count Type Size
Data Record
0 zero_doppler_time
First Zero Doppler Azimuth time of the wave cell. Time of first range line in the SLC Imagette MDS described by this data set
MJD 1 mjd 12 byte(s)
1 quality_flag
Quality Indicator.

(-1 for blank MDSR, 0 otherwise)

flag 1 BooleanFlag 1 byte(s)
2 range_spectral_res
Range spectral bin size of the cartesian cross spectrum
- 1 fl 4 byte(s)
3 az_spectral_res
Azimuth spectral bin size of the cartesian cross spectrum
- 1 fl 4 byte(s)
4 spare_1
Spare
- 1 SpareField 4 byte(s)
5 spec_tot_energy
Spectrum Total Energy
- 1 fl 4 byte(s)
6 spec_max_energy
Spectrum Max Energy
- 1 fl 4 byte(s)
7 spec_max_dir
Direction of Spectrum Max (deg)

Direction is given clockwise from north in the direction the wave propogates

deg 1 fl 4 byte(s)
8 spec_max_wl
Wavelength of Spectrum Max (m)

On higher resolution grid.

m 1 fl 4 byte(s)
9 az_image_shift_var
Variance of the azimuth image shift caused by the orbital velocity
m^2 1 fl 4 byte(s)
10 az_cutoff
Azimuthal Clutter Cut-off wavelength (m)
m 1 fl 4 byte(s)
11 nonlinear_spectral_width
Spectral width of the non-linear part of the cross spectra
m 1 fl 4 byte(s)
12 image_intensity
Image Intensity
- 1 fl 4 byte(s)
13 image_variance
Normalised image variance
- 1 fl 4 byte(s)
14 spare_2
Spare
- 1 SpareField 56 byte(s)
15 min_spectrum
Min value of ocean wave spectrum
m^4 1 fl 4 byte(s)
16 max_spectrum
Max value of ocean wave spectrum
m^4 1 fl 4 byte(s)
17 spare_3
Spare
- 1 SpareField 8 byte(s)
18 wind_speed
Wind speed used in the wave spectra retrieval (m/s)
m/s 1 fl 4 byte(s)
19 wind_direction
Wind direction used in the wave spectra retrieval.

(clockwise from north from where the wind from if confidence is 0, relative to range otherwise) (deg)

deg 1 fl 4 byte(s)
20 norm_inv_wave_age
Normalised inverse wave age
- 1 fl 4 byte(s)
21 SAR_wave_height
SAR swell wave height
m 1 fl 4 byte(s)
22 SAR_az_shift_var
Variance of the azimuth shift computed from the SAR swell wave spectra
m^2 1 fl 4 byte(s)
23 backscatter
Radar backscatter cross section
dB 1 fl 4 byte(s)
24 confidence_swell
Confidence measure of the swell inversion. 0 = inversion successful (a unique spectrum in terms of propagation direction); 1 = inversion not successful (symmetric spectrum)
- 1 us 2 byte(s)
25 signal_to_noise
Average signal-to-noise ratio
- 1 fl 4 byte(s)
26 radar_vel_corr
Radar velocity off-set correction
m/s 1 fl 4 byte(s)
27 cmod_cal_const
Geophysical Calibration constant - CMOD
- 1 fl 4 byte(s)
28 confidence_wind
Confidence measure of the wind retrieval. 0 = external wind direction used during inversion; 1 = external wind direction not used during inversion.
- 1 us 2 byte(s)
29 spare_4
Spare
- 1 SpareField 24 byte(s)
30 ocean_spectra
Ocean Wave Swell spectra polar grid.

Number of bins in wavelength and direction defined in SPH (nominally 24 by 36). Arranged as 24 wavelength cells from longest to shortest wavelength, for zero degrees, then 10 degrees, up to 350 degrees (i.e clockwise direction).

- uc 1 byte(s)
Record Length : 196

DS_NAME : Ocean Wave Spectra



Format Version 114.0  

The ocean wave spectrum is given in the MDS as real samples distributed on a polar grid. The size of the ocean wave spectrum grid is given in the SPH . Typically this will be 24 by 36 bins in wavelength and direction respectively.

The ocean wave spectrum values shall be stored in an unsigned integer format, each part linearly scaled to the maximum and minimum values of the representation (e.g., 0 to 255). The original maximum and minimum values are reported.

The detected spectrum statistics are derived from a high-resolution polar spectrum, prior to encoding for output to the product, or at other intermediate stages of the processing.

If the processor is unable to produce the ocean wave spectra for a given wave cell, the MDSR is time stamped with the time that the ocean wave spectra would have corresponded to, the Quality Flag is set to -1, and the MDSR data fields are all set
to zero.