Task 4 - Validation: Progress Meeting 2

R. Siddans, B. Kerridge, Jane HurleySTFC Rutherford Appleton Laboratory

WBS

Task Overview

Outline of Talk

• TCCON/MLO L2 Comparisons– TCCON, GOSAT

• MLO Case Study– Mauna Loa in-situ – monthly and interannual dependencies

• Pixel/Scan Dependence Metop-A/-B– Closest pixels– Inter-pixel and inter-scan angle dependence

• Cloud Contamination– RAL flag, AVHRR, IASI L2

• Summary

TCCON/GOSAT L2 Comparisons

TCCON sites

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – CH4 VMRs

f=1+0.0023*(day_since_start_of_2009)/365.25

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – CH4 VMRs (day only)

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – number of measurements

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – errors

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – scatterplots

IASI vs. TCCON

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – scatterplots

IASI vs. GOSAT

TCCON/GOSAT L2 Comparisons

IASI vs TCCON & GOSAT – summary

IASI vs. TCCON vs. GOSAT: good correlation (up to 95.5%) between measurements <200 km of TCCON sites, with current IASI retrieval scaled to reflect increase of 0.23%/year of N2O (update in retrieval TBD).

MLO Case Study

IASI vs MLO – monthly averages

MLO Case Study

IASI vs MLO – yearly consistency

MLO Case Study

IASI vs MLO – correlation

MLO Case Study

IASI vs MLO – monthly averages

N2O fixed

CH4 corrected post-hoc

N2O corrected in retrieval (2010-2011 still running…)

MLO Case Study

IASI vs MLO – summary

Mauna Loa: fair correlation (63-81%) between Jan. 2008 - Dec.2012 IASI (<200 km of Mauna Loa) and MLO in-situ measurements taken. MLO in-situ dataset is correlated by 70-95% from year-to-year, whereas the IASI dataset correlates between 15%-85% from year-to-year. Inter-annual variability (comparing month-to-month in nearby years) in CH4 at Mauna Loa is about 0.02 ppmv, which is less than the intra-annual variability (about 0.06 ppm).

Pixel/Scan Dependence Metop-A/-B

Metop-A vs. Metop-B - nearest-pixel

Pixel/Scan Dependence Metop-A/-B

Metop-A vs. Metop-B – retrieval products

Pixel/Scan Dependence Metop-A/-B

Metop-A vs. Metop-B – pixel dependence

CH4 concentrations Other retrieved parameters

Day/night ocean/land separated

Pixel/Scan Dependence Metop-A/-B

Metop-A vs. Metop-B – scan angle dependence

CH4 concentrations Other retrieved parameters

Day/night, ocean/land separated

Pixel/Scan Dependence Metop-A/-B

Metop-A vs. Metop-B – summary

Retrieval products: Pixel-by-pixel analysis shows that 82% of collocated Metop-A and –B measurements gave retrieved CH4 within retrieval error of each other, with a 70% correlation overall. The global distribution analysis showed that the mean difference globally between Metop-A and –B distributions was less than 0.00017 ppmv with a standard deviation of less than 0.008 ppmv.

Products consistency: Slight dependence between IASI pixels/scan angles and the retrieval products (0.008 ppmv and 0.007 ppmv respectively). Error on individual retrievals ~0.03 ppmv, but many individual retrievals averaged in this analysis.

Cloud ContaminationComparison of different flags

Cloud ContaminationStratification with cloud fraction

Cloud ContaminationSummary

The effect of cloud contamination on the retrieved concentrations of CH4 assessed using • the cloud fraction retrieved within the RAL retrieval • the cloud fractions from AVHRR/3• the cloud fraction from IASI L2 products.

The three sets of cloud fractions are uncorrelated.

The concentration of retrieved CH4 generally becomes increasingly scattered over the full 1.65-1.85 ppmv range as the cloud fraction increases, with the average retrieved CH4 column-average VMR unchanged from 1.75 for all cloud fractions.

• TCCON & GOSAT L2 comparison (up to 96% correlation)• MLO case study: fair correlation IASI/MLO (63-81%).

- interannual variability 0.02 ppmv - intra-annual variability 0.06 ppmv

• Retrieval products: Pixel-by-pixel analysis shows that 82% of collocated Metop-A and –B measurements gave retrieved CH4 within retrieval error of each other, with a 70% correlation overall

• Product consistency: Slight dependence between IASI pixels/scan angles and the retrieval products (0.008 ppmv and 0.007 ppmv respectively). Error on individual retrievals ~0.03 ppmv, but many individual retrievals averaged in this analysis.

• Cloud contamination: increases scatter on retrieved CH4, but doesn’t alter mean XVMR retrieved.

Summary