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ANALYSIS OF GLOBAL WAVEFORM RECOVERY FROM ENVISAT RA-2

ANALYSIS OF GLOBAL WAVEFORM RECOVERY FROM ENVISAT RA-2. P.A.M. Berry, M.Dowson & J.D. Garlick. Data processing.

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ANALYSIS OF GLOBAL WAVEFORM RECOVERY FROM ENVISAT RA-2

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  1. ANALYSIS OF GLOBAL WAVEFORM RECOVERY FROM ENVISAT RA-2 P.A.M. Berry, M.Dowson & J.D. Garlick

  2. Data processing We obtained parts of cycle 10 and cycle 11 SGDR data with gaps in both cycles: a continuous sequence was possible from 12 October 02 to 17 November 02 so these are the data used for this analysis. Sufficient data to form this series were received on the afternoon of Thursday 20 March 2003. All data were processed through the expert system to generate the global statistics files required to tune the expert system for Envisat waveforms in both Ku and S band. First tuning was completed on Monday 24 March. Data were then reprocessed globally in both Ku and S band. Processed data were output on the afternoon of Tuesday 25 March, and the first global all-surface waveform statistics were produced. These are summarised on the following slides. Note that the ten range retrackers could not be tuned in time; each requires 1-2 working days to calibrate.

  3. The following series of images contain statistical waveform analysis information calculated for each 1 degree square of the earth’s surface for both Ku and S band. All surfaces are included in the analysis. Information as numerical counts is presented for number of accepted waveforms (those successfully processed), and number of waveforms rejected for no leading edge. Number of waveforms collected in each mode is also shown as a numerical count. Percentages (of total waveforms processed ) are shown for a selection of the individual retrackers. Note that the waveform analysis software is now tuned for Envisat: only the height retracking is still to be tuned.

  4. Number of successfully captured waveforms per 1 degree square for S (a) and Ku_all_modes (b) band (range 0 - 1000 counts) Note the low numbers over rough topography/ mountainous terrain but successful retrieval of some data. Poor counts over the Amazon & Congo basins c.f. ERS ice mode. (a) (b)

  5. Number of points rejected for no leading edge per 1 degree square for S (a) and Ku (b) band (range 0 - 1000 counts) Note missing orbits of S band OK waveforms. Performance in both bands, especially Ku band, shows anomalously poor waveform recovery over inland water: see Amazon and Congo basins. China also poor. (a) (b)

  6. Number of points in 80MHz mode Ku band Some data over rougher terrain in 80MHz mode although generally lower numbers. Note complete absence of data over Amazon, Mesopotamia (S American one!) Congo, Ganges etc. Hence problem - snagging on inland water targets needs 80MHz mode

  7. Number of points in 320MHz mode Ku band Most data in 320 MHz mode. But note zero (white) individual squares over Andes and Himalayas where no data successfully acquired in 320 MHz mode

  8. Number of points in 20MHz mode Ku band As expected, turning on over extreme terrain. Also over some less obvious areas - strange patches in Africa and South America and across Asia not well correlated with terrain. Needs investigation.

  9. Percentage of wide waveforms (a) S band (b) Ku band all modes As expected, some fat waveforms over ocean due to high sea state especially S band fatter waveforms; this consistent with Topex C/Ku band behaviour. Detection of land ice and deserts in both bands. (a) (b)

  10. Percentage of wet type waveforms (a) S band, (b) Ku band all modes Unlike ERS and Topex data, Envisat wet echoes do not preferentially show inland water locations by high percentages. This appears to be because so many wet echoes are not successfully acquired. More investigation is URGENTLY required. (a) (b)

  11. A wealth of detailed spatially correlated information present in both bands. Unfortunately, this reflects a far worse performance than ERS 1/2: also worse than Topex except over mountains. VERY high incidence of incomplete waveform recovery over wet terrain!!!. Ganges, Amazon, Mississippi, Congo, Holland, India….. Incompletely acquired waveforms (a) S band (b) Ku band all modes (a) (b)

  12. Ocean like (desert) waveforms (a) S band (b) Ku band all modes As expected, desert retracker picks up much ocean data: less of fatter S band waveforms. Deserts as expected in both bands, similar to ERS ocean mode and to Topex in C and Ku bands but clearer delineation. (a)

  13. Most data are in ocean mode over land. ERS 1/2 and Topex showed this is not appropriate, even 128 bins insufficient width to acquire both the slope components and the nadir part of the returns. This is a function of the terrain, NOT the tracker!! This is critically affecting inland water waveform recovery. Incompletely acquired waveform plots devastating, especially in Ku band. S band slightly better: may have to discard Ku band for inland water monitoring if this problem is not addressed. This is because instrument in ocean mode is tracking slope components and missing nadir echoes. Strong evidence that mode switching algorithm is not changing mode appropriately over land. Ridiculously short time for data analysis prior to meeting prevented detailed analysis of mode-switching performance, this will be done over the next few weeks. Retrieval of data over Himalayas and Andes shows superb potential of this instrument for land applications. Currently this potential is NOT REALISED. Discussion

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