An Update on A Few Issues Relevant to Ocean Salinity Retrieval for SMOS Joe Tenerelli SMOS Quality Working Group 11 July 4-5 2013 ESA ESRIN

An Update on A Few Issues Relevant to Ocean Salinity Retrieval

for SMOS

Joe TenerelliSMOS Quality Working Group 11

July 4-5 2013ESA ESRIN

PLAN

Part 1: Review of celestial sky map errors and the potential impact upon the ocean biases.

Part 2: Review of the impact of Level 1 Version 601 on ocean biases.

Part 3: Review of impact of the All-LICEF approach on ocean biases.

Part 1:

On the Errors in the Celestial Sky Brightness Maps for SMOS and AQUARIUS

CELESTIAL SKY BRIGHTNESS AT L-BAND

From: http://en.wikipedia.org/wiki/Celestial_sphere

Radiation from distant sources incident at earth’s surface…

Images taken from: http://hyperphysics.phy-astr.gsu.edu/hbase/eclip.html

Need a coordinate system to describe this radiation: Use equatorial coordinates (spherical)


The celestial sky radiation is the sum of unpolarized cosmic microwave background radiation (2.7), hydrogen line emission (up to around 3 K) and continuum emission (dominant along the galactic equator):

+ =CMB+continuum

totalHydrogen line emission


SUMMARY OF PROBLEMBelow are the two skymaps, one from ESA and the other from NASA, that are currently used for analyzing SMOS data. They have been produced by combining the cosmic microwave background, continuum, and hydrogen line emission contributions. The ESA map is documented to be in B1950 equatorial coordinates (EC) while the NASA map is documented to be in J2000 equatorial coordinates. There is a shift of about .64o in right ascension between these two coordinate systems. Here we have remapped the NASA map into B1950 EC.

ORIGINAL ESA MAP IN B1950 EC ORIGINAL NASA MAP IN B1950 EC

SUMMARY OF PROBLEM

Unfortunately, it appears that, up to this point, these ESA and NASA sky maps for the 19 MHz MIRAS bandwidth have contained significant systematic errors that reach several kelvin in the first Stokes parameter divided by two. Compared to the ‘correct’ sky map for MIRAS, the error maps (first Stokes parameter divided by two) are shown below in B1950 equatorial coordinates.

ESA MAP ERROR NASA MAP ERROR

The error in the ESA sky map is mostly related to an inversion of the hydrogen line contribution in galactic latitude and longitude, before transformation into equatorial coordinates:

From: http://en.wikipedia.org/wiki/Celestial_coordinate_system

Transformation of hydrogen line contribution from galactic to equatorial coordinates required before adding to the continuum map.

Original version of Floury HI line map in B1950 equatorial coordinates:

NASA SMOS 19 MHz HI line map in B1950 equatorial coordinates. This version is inverted in both galactic latitude and longitude relative to the Floury HI line map. This map shows the correct orientation:

Second version of Floury HI line map in B1950 equatorial coordinates. This one is still erroneously inverted in galactic latitude:

Most recent (and best) version of Floury HI line map in B1950 equatorial coordinates:

Original version of Floury HI line map – NASA SMOS HI line map (Th+Tv)/2 in B1950 equatorial coordinates:

Second version of Floury HI line map – NASA SMOS HI line map in B1950 equatorial coordinates:

Third (latest) version of Floury HI line map – NASA SMOS HI line map in B1950 equatorial coordinates. Much better but there is still a small systematic difference the maps.

This systematic difference is more clear if we reduce the range of the color scale:

Latest Floury HI line map– NASA SMOS HI line map in B1950 equatorial coordinates. This map differs from that of the previous slide in that here I have transformed the HI line contribution from galactic to B1950 equatorial coordinates myself using a transformation that agrees exactly with independent sources available on the internet. The residual systematic differences seem to be reduced further.

THE CONTINUUM MYSTERYThe sky maps for the Aquarius and SMOS missions are provided in equatorial coordinates, with spherical coordinates named ‘right ascension’ and ‘declination’. Below is the total sky brightness map in ‘B1950’ equatorial coordinates:

THE CONTINUUM MYSTERYThe ‘B1950’ refers the the reference direction used to define the equatorial coordinate system. The reference direction is defined to correspond to the vernal (or northern hemisphere spring) intersection of the earth orbital and equatorial planes, as shown below. Owing to precession (and to a much smaller extent nutation, or ‘wobbling’), this reference direction shifts slowly relative to the stars, and so it is necessary to specify a date at which the intersection is taken. Two common references are B1950 (reference direction taken at the beginning of the Besselian year 1950) and J2000 (reference direction taken at the beginning of the Julian year 2000). Additionally, the coordinate system reference direction may or may not take into account nutation. If it does, then the coordinate system is referred to as ‘true of date’, otherwise it is referred to as ‘mean of date’.

Images taken from: http://hyperphysics.phy-astr.gsu.edu/hbase/eclip.html

THE CONTINUUM MYSTERYThe transformation from B1950 to J2000 equatorial coordinates is mainly a shift of less than 1o in right ascension:

THE CONTINUUM MYSTERYNow the discrepancies shown in the preceding slides involve only the hydrogen line emission. It turns out that the continuum maps agree perfectly away from Cassiopeia when the maps are compared with no coordinate transformations applied. This is surprising because the NASA map is documented to be in J2000 EC while the ESA map is documented to be in B1950 EC.

NASA CONTINUUM TRANSFORMED TO B1950 EC (ESA B1950 EC)-(NASA B1950 EC)

STRANGE: THE DIFFERENCE MAP ON THE RIGHT SHOULD BE ZERO AWAY FROM CASSIOPEIA!

Cassiopeia

THE CONTINUUM MYSTERY

NASA CONTINUUM IN DOCUMENTED J2000 EC (ESA B1950 EC)-(NASA J2000 EC)

INSTEAD, THE NASA MAP IN DOCUMENTED J2000 EC MATCHES THE ESA MAP IN B1950 EC!

Cassiopeia

Differences in the preceding slides involve only the hydrogen line emission. It turns out that the continuum maps agree perfectly away from Cassiopeia when the maps are compared with no coordinate transformations applied. This is surprising because the NASA map is documented to be in J2000 EC while the ESA map is documented to be in B1950 EC.

ESA – STOCKERT CONTINUUMTo determine the coordinate system of the ESA and NASA continuum maps, the original Stockert continuum maps for the northern sky in both B1950 and J2000 EC were downloaded and compared to both the ESA and NASA continuum maps in their original coordinate systems (B1950 EC for the ESA map and J2000 EC for the NASA map). Below we show the comparison for the ESA continuum map. Obviously the ESA continuum agrees with the B1950 EC Stockert map away from two areas where the Stockert data have been deliberately modified.

(ESA)– (STOCKERT IN J2000 EC)

Northern and southern sky map overlap

(ESA)– (STOCKERT IN B1950 EC)

Cassiopeia

NASA– STOCKERT CONTINUUMSurprisingly, the NASA continuum map also agrees with the B1950 EC Stockert map away from Cassiopeia and the declination range where the southern survey information was apparently introduced. This is surprising because the NASA map is documented to be in J2000 EC, not B9105 EC. But the continuum portion is obviously in B1950 EC. In fact it is identical to the ESA continuum away from Cassiopeia. Unfortunately; because the HI component is is J2000EC, the total NASA skymap is the sum of the B1950 EC continuum and the J2000 HI maps, which is not a consistent sum. Therefore the total sky map is erroneous.

(NASA)– (STOCKERT IN J2000 EC)

Northern and southern sky map overlap

(NASA)– (STOCKERT IN B1950 EC)

Cassiopeia

The following four slides show the original ESA sky map, followed by the two best ESA maps and, finally, the NASA map for the MIRAS bandwidth of 19 MHz. The current ‘best’ map is the third slide and you can flip between the slides to compare.

All maps show the first Stokes parameter divided by two for the total sky brightness (CMB, continuum, and 19 Mhz hydrogen line emission).

The original map from Floury with HI line map flipped in both galactic latitude and longitude:

The most recent map from Floury with HI line map correctly oriented but with a very small distortion relative to the NASA HI line map:

The most recent map from Floury with HI line map correctly oriented and adjusted to remove the remaining distortion relative to the NASA HI line map:

The NASA sky map with the J2000 EC HI line map erroneously added to the B1950 EC continuum map:

The following two slides show the errors in the original ESA sky map and the current NASA map for the MIRAS bandwidth of 19 MHz, relative to the current ‘best map’.

The maps show the error in the first Stokes parameter divided by two.

The error in the original ESA sky map involves error all along the galactic equator with too little brightness near the brightest portion of the galaxy:

The error in the current NASA map is mostly a shift of the map to smaller right ascension. Rough surface scattering will tend to smooth this out and reduce the error:

Potential Impact of Sky Map Errors on Bias Calculations

Caveats:

• Impact assessed by comparing results using NASA and ESA sky maps.

• Done before we knew the NASA map is wrong too.

• Ned to reevaluate using the correct sky map.

OLD GALACTIC (DPGS MAP)

NEW GALACTIC (NASA SKY MAP)

OLD GALACTIC (DPGS MAP)

NEW GALACTIC (NASA SKY MAP)

IMPACT HARDLY VISIBLE AFTER INTEGRATION FROM 40oS to 5oN:

CONCLUSIONS FOR PART 1

1. Both the ESA and NASA sky maps have contained errors of up to several kelvin in the first Stokes parameter divided by two up to this point. There errors in the two maps have different origins and the spatial patterns of the errors differ.

2. Impact on bias analyses appears to be minimal based upon comparing biases derived from the ESA and NASA sky maps. Must reevaluate this conclusion with the correct sky map.

Part 2:

Comparing the Operational and Level 1 V601 Solutions in Terms of Bias over the

Ocean

Many changes in V601 relative to current operational Level 1 Processor, but two key changes are:

1. L1 is fixed (at 0.15 dB) rather than computed using the 1-slope model;

2. Only NIR CA is used for the zero baseline rather than both NIRs BC and CA.

We will examine the impact of these changes on 76 eastern Pacific half-orbits (38 ascending and 38 descending) from June 2010 to January 2013.

COMPARING OPERATIONAL AND V601 LEVEL 1 BIASES OVER THE OCEAN

In terms of ascending and descending passes separately, with biases averaged between 40oS and 5oN:


Descending-ascending passes, with biases averaged between 40oS and 5oN. V601 descending pass drop late in year is about half that for the operational L1:


Comparing NIR TA and corresponding AF-FoV biases, averaged between 25oS and 5oN. Good correspondence for ascending passes.



Correspondence for descending passes is not as good late in the year, with descrepancies between NIR TA and AF-FoV biases reaching up to 0.4 K. For V601 the seasonal cycle in NIR CA is smaller than in NIR CA, but the interannual drift is larger for NIR BC.

Descending-ascending pass AF-FoV biases averaged between 25oS and 5oN. Magenta curve shows impact of V601 relative to operational L1:



If we overlay in cyan the difference between V601 NIR TA and operational TA the curve matches very closely the AF-FoV curve:

The desc-asc bias differences V601-Operational follow closely the desc-asc Tp7 curve in green. Presumably this just reflects the impact of the loss model in the operational results:



1. V601 antenna and brightness temperatures do exhibit noticeably different trends relative to operational data.

2. For V601 the seasonal cycle in NIR BC is smaller than in NIR CA, but the interannual drift is larger for NIR BC.

3. Maybe slightly more consistency in desc and asc for V601 than for operational L1.

4. Differences in AF-FoV seem to reflect mostly changes in NIR TA as well as the use of different subsets of NIRs for the zero baselines.

5. Is one set of solutions ‘better’ than the other? Hard to say now. Will be good to look at hovmoller plots when we have a more complete set of data for V601.

Part 3:

Comparing the Operational and All-LICEF Solutions in Terms of Bias over the Ocean

R. Oliva, J. Gourrion, J. Tenerelli, V. Gónzalez, I. Corbella

• MTS has been used to process data from L0 up to level1A

• L1A REPRO/DPGS products are overwritten using MTS level1A data:– Calibrated visibilities are directly overwritten (Calib_Visib) – NIR_Brightness_Temp

NIR-H -> mean Ta LICEF of nearest snapshot in HH polarizationNIR-V -> mean Ta LICEF of nearest snapshot in VV polarizationT3 and T4 are overwritten with Re[Vzb] and Im[Vzb],

respectively

• From L1A to L1B -> L1PP release 500– Sun correction applied– Latest versions of auxiliary files and G and J –matrices (no cross-polar

terms) compatible with version 500

• Orbits selection: based on selection of ANX longitude value – One ascending / one descending overpass per day– Match set of overpasses with data available from nominal processing

All-LICEF processing summary

COVERAGE OF HALF-ORBITS SELECTED FOR ALL-LICEF TEST

Bias in Descending passes

NOMINAL BIAS (TEST PASSES)

ALL-LICEF BIAS (TEST PASSES)

ALL-LICEF – NOMINAL difference

FOCUS on TEMPORAL (Removing a mean value computed over all dates and latitudes)



FOCUS on TEMPORAL (Removing a mean value computed over all dates and latitudes)

NOMINAL and ALL-LICEF comparison

Integrated over [40ºS, 5ºN]

FOCUS on LATITUDINAL (Removing a mean value computed for each date and [20ºS,20ºN] )



FOCUS on LATITUDINAL (Removing a mean value computed for each date and [20ºS,20ºN] )

Ascending – Descending

NOMINAL BIAS (ALL PASSES)




Ascending passes




All-LICEF solutions exhibit smaller seasonal and interannual trends trends than 1-slope L1 solutions for descending passes.

For ascending passes All-LICEF shows smaller internannual drift amplitude but similar seasonal drift amplitude.


All-LICEF solutions exhibit the same orbital drift as those from the current operational L1 (using NIRs BC and CA for the zero baseline):



1. All-LICEF solutions exhibit smaller seasonal and interannual trends trends than 1-slope L1 solutions for descending passes.

2. For ascending passes All-LICEF shows smaller internannual drift amplitude but similar seasonal drift amplitude.

3. Short term (orbital) drift is similar in both solutions. Eclipse bias is present in both. No advantage to All-LICEF for orbital drift.

EXTRA SLIDES:

IMPACT OF DIRECT SUN AND SUN GLINT ON NIR ANTENNA

TEMPERATURE BIASES

• Fixed L1=0.15 dB• No direct or reflected sun in forward model

IMPACT OF THE SUN ON THE NIR BIASES

NIR BC NIR CA

• Fixed L1=0.15 dB• Direct but no reflected sun in forward model


NIR BC NIR CA

• Fixed L1=0.15 dB• Direct and reflected sun in forward model


NIR BC NIR CA

• 1-Slope model for L1• No direct or reflected sun in forward model


NIR BC NIR CA

• 1-Slope model for L1• Direct but no reflected sun in forward model


NIR BC NIR CA

• 1-Slope model for L1• Direct and reflected sun in forward model


NIR BC NIR CA

EXTRA SLIDES:

IMPACT OF PERMITTIVITY MODEL ON AF-FOV BIASES

Possible impact of permittivity model: Bias derived using Meissner and Wentz 2012 minus that derived using Klein and Swift 1977:

IMPACT OF PERMITTIVITY MODEL ON THE AF-FoV BIASES

Documents

An Update on A Few Issues Relevant to Ocean Salinity Retrieval for SMOS Joe Tenerelli SMOS Quality Working Group 11 July 4-5 2013 ESA ESRIN