Envisat: Near Real Time Processing
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Envisat: Near Real Time Processing and Oceanography. Envisat CCVT Meeting. Kirk Whitmer Gregg Jacobs JE Sverdrup/NRL Stennis Space Center, MS, USA. ALPS and ODDITIES. ALPS : Near real time data processing system Data is quality checked at each step and suspect data is flagged

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Envisat: Near Real Time Processing and Oceanography

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Envisat: Near Real Time Processing

and Oceanography

Envisat CCVT Meeting

Kirk Whitmer

Gregg Jacobs

JE Sverdrup/NRL

Stennis Space Center, MS, USA


ALPS and ODDITIES

  • ALPS: Near real time data processing system

  • Data is quality checked at each step

  • and suspect data is flagged

  • Must err on the side of caution because of

  • subsequent subsystems

  • Run daily at NRL and NAVO

  • ODDITIES: Graphical data analysis system

  • Results displayed on

    The Real Time Ocean Environment website

  • www.ocean.nrlssc.navy.mil/altimetry

  • Run daily at NRL

Envisat imar data fed into the systems…


read: data is read from gdrs

into ALPS format

  • Smooth electromagnetic bias and

  • wet troposphere along track

  • Apply correction terms to height:

  • Wet troposphere, Dry troposphere

  • Inverse barometer, Solid tide

  • Ionosphere, Electromagnetic bias

  • Check for minimum number of high rate values (>15)

  • Check flag for water (sea ice?)


Ionosphere drop plot

Ku band correction only

Doris Ku band correction only

All ionosphere corrections applied:

Ku band correction

Doris Ku band correction

Model Ku band correction


interp: data is interpolated to

reference ground tracks

  • Minimum number of points needed to interpolate

  • Interpolation incorporates the geoid gradient

  • Along track smoothing


  • Data too sparse to interpolate to ground tracks

  • Single largest contributor to “dropped” data points


aptide:tides are removed

  • got00.2 tide model applied

  • No points are dropped


orbgem:orbit correction calculated

and applied

  • Long term mean and climactic mean removed

  • Iterative sinusoidal fit calculation

  • Return means

  • Apply correction based on fit


Orbit correction magnitude

Mean: 60.7 cm

RMS: 74.0 cm


  • Even after orbit correction, still considerable noise.


apply: mean removed

  • Along track “box car” filter

  • Sanity checks


Sea ice issue?

High latitude makes

ice more important

Detection algorithm

or flag desireable

SSH anomaly plot suggests many

sea ice points remaining


ERS-2

GFO


  • Jason-1

  • Multiple causes for ice point drops

  • Lower latitude reduces importance


Percent data utilized

Jason (osdr)84.73/85.20 %

Jason (igdr)90.17/90.17 %

Ers-284.22/90.26 %

GFO (doppler)87.49/87.49 %

GFO (laser)90.30/90.30 %


Sea Surface Height Anomaly

14 October 2002


Altimeter cross track intercomparisons

  • High latitude values sea ice influenced


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