DPGS OTT strategy analysis

SMOS L2 Ocean Salinity

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DPGS OTT strategyanalysis

4 February 2013

ARGANS


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Background

• OTT are generated for DPGS monthly, using 10 ascending and 10 descending

South Pacific operational L1c orbits

• Use data from stable salinity regions

• Reference TBs generated by forward model using climatology

• Time series for salinity anomalies (SSS - climatology) for this region should be

stable if OTT are correcting drift – but we see nearly ±1 psu. Why?

Alignment? OTT quality?


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South Pacific region

Climatology for South Pacific test site 1: stable salinity (36.4 ±0.1 psu)

www.argans.co.uk/smos/pages/regional/webform0.php


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OTT alignment in DPGS

OTTs made from orbits selected from first ~6 daysTypically deployed around 12th of each month

~24 day delay compared to ideal validity

20 orbits

-> OTT1

1 6 3012 18 24 1 6 3012 18 24

OTT#1 in DPGS

3

20 orbits

-> OTT2

327

OTT#2 in DPGS

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Optimal OTT#2 validity


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Methodology

• Select DPGS L1c orbits for 2012 with > 1000 grid points in South Pacific region

122 (as used in PPEP/PPSR & web time series)

• longitude 120 to 130 west, latitude 15 to 25 south

• 300 ascending & 300 descending orbits

• Process with L2OS v550 and:

• monthly OTT as used by DPGS (nominal reference)

• same monthly OTT as used by DPGS with optimal temporal alignment

(24 day shift)

• weekly NIR aligned 2011 REPR OTT (optimal alignment)

• MOTT for 2011

• Extract average filtered SSS1 time series for nGridPoints > 1000


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OTT strategy: ascending orbits

Monthly DPGS OTTs: 12 day delaySSS1 std = 0.36 (filtered by quality)


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DPGS 9 day SSS1 anomaly (filtered by flags)


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OTT sun in EAFFOV


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Monthly DPGS OTTs with optimal deploymentSSS1 std = 0.24 (filtered by quality)


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delta = optimal - monthly


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Ascending orbits

• OTTs shifted by 24 days (optimal validity) give lower salinity anomalies in both

ascending & descending (std decreases from 0.36 to 0.24)

TEC not a factor (low in ascending)

• Looks like a sun effect

sun appears in EAFFOV May, disappears July

sun in back September/October?

• Impact of filtering...


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Monthly DPGS OTTs: 12 day delaySSS1 std = 0.36 (filtered by flags)


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Monthly DPGS OTTs: 12 day delaySSS1 std = 0.36 (filtered by quality, > 1000 grid points)


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Monthly DPGS OTTs: 12 day delaySSS1 std = 0.40 (filtered by quality, > 500 grid points)


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Monthly DPGS OTTs: 12 day delaySSS1 std = 0.44 (filtered by quality, all grid points)


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Ascending orbits


ascending & descending (std decreases from 0.36 to 0.24)


• Looks like a sun effect

sun appears in EAFFOV May, disappears July

sun in back September/October?

• Filtering by poor flags impacted by galactic flag bug in v550

• Filtering by quality < 150 avoid this bug, but results are comparable

• Fewer grid points in region => more noisy

L2OS product filtering needs further analysis


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OTT strategy: descending orbits

Monthly DPGS OTTs: 12 day delaySSS1 std = 0.48 (filtered by flags, including GN bug)


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Monthly DPGS OTTs: 12 day delaySSS1 std = 0.48 (filtered by flags, including GN bug)

Galactic noise September-October


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Filtering by quality removes impact of galactic noise


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DPGS 9 day SSS1 anomaly (filtered by flags)


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OTT sun in EAFFOV OTT sun in EAFFOV


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DPGS OTTs with optimal deploymentSSS1 std = 0.28 (filtered by quality)


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delta = shifted - DPGS


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Summary


ascending (std 0.36 -> 0.24) & descending (std 0.41 -> 0.28)


Low impact of galactic noise in September/October in descending orbits

(GN bug reduces the number of valid points)

• How can the ‘optimal’ OTTs be improved?

Delayed production

Increased OTT frequency


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Yin et al. IGARSS 2012

Mean OTTs Along dwell lines

Galactic noise

Temporal evolution of OTT and galactic noise anomalies (averaged along dwell lines) across the satellite track, Ascending orbits

ξ

ξ

ξ

No clear correlations between temporal across track variations in OTT and in galactic noise

20100501

20120501

20100501

20120501

2K

-2K

2K

-2K


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Galactic noise

No clear correlations between temporal across track variations in OTT and in galactic noise

Temporal evolution of OTT anomalies (averaged along dwell lines) across the satellite track, Descending orbits

Mean OTTs Along dwell lines

20100501

20120501

20100501

20120501

2K

-2K

2K

-2K


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OTT strategy: DPGS


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OTT means

Sun declination

Annual variations Descending orbits

Physical temperature of the antenna patches

(Tx+Ty)/2

with Sun in FOV

with Sun in FOV

AF

EAF


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Sun declination

Annual variations Ascending orbits

Physical temperature of the antenna patches

(Tx+Ty)/2

with Sun in FOV

with Sun in FOV

OTT means


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Case (No. Of OTTs) Region R p-values

Asc. Without Sun (28)AFFOV 0.152 0.440

EAFFOV 0.233 0.233

Asc. With Sun (16)AFFOV -0.347 0.188

EAFFOV -0.382 0.144

Asc. All (44)AFFOV -0.110 0.478

EAFFOV -0.124 0.424

Desc. Without Sun (13)AFFOV -0.343 0.229

EAFFOV -0.302 0.316

Desc. With Sun (31)AFFOV -0.931 2.26*10-13

EAFFOV -0.616 7.49*10-4

Desc. All (44) AFFOV -0.925 2.89*10-19

EAFFOV -0.649 1.90*10-6

Correlation coefficients between OTTs and <Tp7> and p-values for testing the hypothesis of no correlation (only p-values less than 0.05 correspond to significant R; other values are indicated in italics)


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OTT strategy: DPGS

ascending

descending


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OTT strategy: optimal

ascending

descending


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Way ahead

•Delay DPGS salinity products?

Need a minimum of 24 days delay if OTT generated monthly

•Generate OTT more frequently?

Additional work for preparation, ingestion & monitoring

Still not optimal (offset)

•Implement an OTT post-processor?

L2OS can output data for OTT post-processing (AUX or in DAP)

OTTs can be generated as a running average daily (or less frequently)

Drift statistics available for monitoring

•MOTT & drift correction derived from delta TBs?


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Work required

•Repeat 2012 study with

v600 L2OS & monthly OTT

OTT made more frequently

OTT running average

different regions of interest

plot L1c TBs, forward model TBs/galactic noise, etc @ TOA

look for correlations with TP6/7...

•Design system for automatically generating OTT within DPGS

•Reprocessing?


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OTT strategy

2011 REPR OTTs (aligned with 2011 NIR events)ascending orbits, filtered by flags


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2011 MOTT (one OTT for all year)ascending orbits, filtered by flags

Documents

DPGS OTT strategy analysis