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ESA CCI Toolbox (Cate)
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Unexpected visual appearance of sea level dataset after coregistration #802

Open HelenClifton opened 5 years ago

HelenClifton commented 5 years ago

Actual behavior

A sea level dataset is coregistered with an SST dataset.

Sea level dataset variable ampl before coregistration:

ampl_before_coregistration

Sea level dataset variable ampl before coregistration:

ampl_after_coregistration

Sea level dataset variable phase after coregistration:

phase_before_coregistration

Sea level dataset variable phase after coregistration:

phase_after_coregistration

@forman, @JanisGailis ,@kjpearson Please investigate. Similar effect is seen when using Cloud or Ozone dataset as the master.

Steps to reproduce the problem

  1. Download / open esacci.SST.day.L4.SSTdepth.multi-sensor.multi-platform.OSTIA.1-1.r1, time range : 2004-01-01, 2004-02-31
  2. Download / open esacci.SEALEVEL.mon.IND.MSLAMPH.multi-sensor.multi-platform.MERGED.2-0.r1
  3. Select coregister, master ds = sst, slave ds = sealevel, other parameters : default

Specifications

cate-2.0.0-dev.20 Windows 7 Professional

kjpearson commented 5 years ago

Unfortunately I can't reproduce this as when I run coregister none of the variables plot onto the globe, they layer is transparant. The same is true for the SST input dataset.

Visually the amplitude plots look a little washed in plot 2 compared to plot 1 (I presume after and before respectively). The phase interpolation might have to be a special case as it is a modulo 360 variable. So the average of 359 and 4 would be 1.5 rather than 181.5

kjpearson commented 5 years ago

I think it's more complicated in fact. This dataset probably need an interpolation of amp x cos(phase) between the cells. I think you would do that by treating it as a complex number (x+iy) where x=amp x cos(phase) y=amp x sin(phase). Interpolate those x and y values and then convert x and y back to amp and phase. Worth checking that with the sea level people.

HelenClifton commented 5 years ago

Some extra information from testing dev.23: same sort of features are seen when coregistering this sea level dataset with following master datasets: esacci.FIRE.day.L4.BA.multi-sensor.multi-platform.MERIS.v4-1.r1 esacci.OC.mon.L3S.K_490.multi-sensor.multi-platform.MERGED.2-0.r1 esacci.OC.mon.L3S.CHLOR_A.multi-sensor.multi-platform.MERGED.2-0.r1 esacci.SOILMOISTURE.day.L3S.SSMS.multi-sensor.multi-platform.ACTIVE.03-2.r1 esacci.SOILMOISTURE.day.L3S.SSMV.multi-sensor.multi-platform.PASSIVE.03-2.r1