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Ground-based FTIR Update CAVIAR Meeting NPL, 29 th September 2010 Tom Gardiner, Marc Coleman.

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Presentation on theme: "Ground-based FTIR Update CAVIAR Meeting NPL, 29 th September 2010 Tom Gardiner, Marc Coleman."— Presentation transcript:

1 Ground-based FTIR Update CAVIAR Meeting NPL, 29 th September 2010 Tom Gardiner, Marc Coleman

2 Sunday, 20 April Summary Aged mirror reflectivity measurements Smoothed calibration function CAVIAR blackbody – uncertainty assessment and paper preparation

3 Sunday, 20 April Aged mirror reflectivity Absolute reflectivity measurements of gold mirror used in solar tracker during Jungfrau campaign now underway. Measurements under ambient conditions just completed. Measurements under different humidity conditions underway.

4 Sunday, 20 April Updated reflectivity results

5 Sunday, 20 April Updated calibration function Latest mirror reflectivity measurements have confirmed transmission properties for both field campaigns and related calibration exercises. Extrapolation outside of reflectivity measurement region has been revisited, and a (hopefully) improved estimate derived. Updated calibrations functions now available that include these revisions, and integrate solar limb darkening effects.

6 Sunday, 20 April Raw Calibration Function (Phase 1 – broadband InSb measurement)

7 Sunday, 20 April Issues with raw function Calibration function should be a smoothly varying function across the the spectral range. Raw function contains lots of high resolution information relating to laboratory water vapour and instrumental noise. This high frequency noise will feed into field results analysis. Particularly the case in the interesting high frequency region Raw function also not suited to re-sampling at different resolutions. Smooth underlying function is visually obvious, but need an analytical method to extract it.

8 Sunday, 20 April Smoothing / fitting procedure Filter raw spectrum using repeated application of a sharp gradient exclusion filter. This removes the effects of the water lines and some high frequency noise. Fit a high order polynominal to the remaining points. This gives an analytical expression for the shape of the calibration curve, that can be applied to any frequency scale within the frequency limits of the original data. Should be particularly useful when ratioing two calibration curves to determine scaling functions for different gains / apertures.

9 Sunday, 20 April Polynominal fit to smoothed calibration curve

10 Sunday, 20 April Residual between smoothed calibration curve and original function

11 Sunday, 20 April CAVIAR Blackbody Now have a write up of the blackbody uncertainties. Covers the various sources of uncertainty including : –Nextel coating reflectance –Cavity emissivity –Ambient reflection –Uniformity –Themometry –Cavity thermal gradient –Thermal gradient across coating –Formal traceability to the SI through AMBER facility This will form the basis for calibration paper.

12 Sunday, 20 April CAVIAR Blackbody Uncertainty Table

13 Sunday, 20 April International Intercomparison CAVIAR blackbody used in first part of CEOS comparison of IR brightness temperature measurements in support of satellite validation : Laboratory and Ocean surface temperature comparison of radiation thermometers. Took part in two stages –Stage 1 took place at NPL and involved laboratory measurements of participants blackbodies calibrated using the NPL reference transfer radiometer (AMBER), while participants radiometers were calibrated using the CAVIAR blackbody. –Stage 2 took place at Rosenstiel School of Marine and Atmospheric Science (RSMAS) and involved laboratory measurements of participants blackbodies calibrated using the NIST Thermal-Infrared Transfer radiometer (TXR), while participants radiometers were calibrated using the RSMAS and NIST water bath blackbodies.


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