Characterization of MKIV Brewer #066 for NO 2 measurements

Transcription

1 Characterization of MKIV Brewer #066 for NO 2 measurements Henri Diémoz Regional Environmental Protection Agency (ARPA) Valle d Aosta (Italy) Sapienza - University of Rome Brewer Users Meeting Beijing, China, September 2011

2 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

3 Major works about Brewer and NO 2 J. B. Kerr, 1989 Hardware changes (MKII MKIV) 1200 mm 1 grating visible at 2nd order Blue Glass filter 2 different modes of operation: o3 and n2

4 Major works about Brewer and NO 2 Since 1989, much work was done about NO 2 and Brewers, e.g. A. Cede developed a new (ds) algorithm to determine the NO 2 content with MKIII D. Barton improved the (zs) technique with MKIV

5 Aim of present research accurately characterize a Brewer MKIV (#066) develop a new DS algorithm for MKIV calibrate Brewer #066 compare the results of ZS and DS techniques using MKIV First step: instrumental characterization

6 Aim of present research accurately characterize a Brewer MKIV (#066) develop a new DS algorithm for MKIV calibrate Brewer #066 no calibrated standard MKIV for NO 2 measurements is available worldwide compare the results of ZS and DS techniques using MKIV First step: instrumental characterization

7 Aim of present research accurately characterize a Brewer MKIV (#066) develop a new DS algorithm for MKIV calibrate Brewer #066 no calibrated standard MKIV for NO 2 measurements is available worldwide compare the results of ZS and DS techniques using MKIV First step: instrumental characterization

8 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

9 Overview of tests Some routines are already available in n2 mode e.g. dt, sl, rs, sh Some other routines need to be adapted e.g. dsp, sc: Not an NO2 routine fi: lamp is too bright in visible

10 Overview of tests Some routines are already available in n2 mode e.g. dt, sl, rs, sh Some other routines need to be adapted e.g. dsp, sc: Not an NO2 routine fi: lamp is too bright in visible

11 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

12 Dispersion test

13 Dispersion test - n2 mode DSP test is used in o3 mode to determine the operational wavelengths and the resolution and calculate appropriate coefficients. In n2 mode, you could simply multiply the dispersion function by 3/2. However, a DSP test in the visible may be useful: to check whether the Brewer is still in focus in the visible or not; to check whether the dispersion function is still valid in the visible or not.

14 Dispersion test - n2 mode Hg, Cd and Zn have useful lines in the visible Ne has no isolated line in the visible continuum of Xe affects the line measurements The updated dsp routine will be included by Volodya in the next release of the Brewer operating software

15 Dispersion test - n2 mode Hg, Cd and Zn have useful lines in the visible Ne has no isolated line in the visible continuum of Xe affects the line measurements The updated dsp routine will be included by Volodya in the next release of the Brewer operating software

16 Dispersion test - focus expected range of FWHM from UV and measured FWHMs in visible(a) slit number

17 Dispersion test - wavelength shifts Method 1 1 run the dsp in o3 mode and determine the dispersion coefficients 2 run the dsp test in n2 mode and determine the step number relative to the center of the lines (Hg, Cd, Zn) 3 compare the nominal wavelengths of the visible emission lines and the wavelengths obtained with the UV dispersion coefficients 3/2 and step numbers from previous test 4 remember that 1 motor step 0.1 A in the visible

18 Dispersion test - method slit 0 slit 1 slit 2 slit 3 slit 4 slit 5 calc - given (A) motor step number

19 Dispersion test - method slit 0 slit 1 slit 2 slit 3 slit 4 slit 5 calc - given (A) motor step number

20 Dispersion test - method calc - given (A) slit 0 slit 1 slit slit 3 slit 4 slit motor step number

21 Dispersion test - wavelength shifts Method 2 1 new routine vi has been developed (λ = nm) 2 you have to transfer the visible calibration from a reference standard (synchronized scans) 3 apply SHICrivm on the measured visible spectra to estimate the wavelength misalignment using the Fraunhofer lines (UV slit function should be multiplied by 3/2) and look at the results

22 Dispersion test - method SHICrivm slit 0 slit 1 slit 2 slit 3 slit 4 slit 5 calc - given (A) motor step number

23 Dispersion test - wavelength shifts 1 both methods give negative values. Why? 2 how are NO 2 measurements affected by a wavelength misalignment? See SC results...

24 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

25 Sun scan test - classical algorithm What about NO 2 measurements? Do the operational wavelengths correspond to a stable point? SC routine was adapted to n2 mode.

26 Sun scan test - classical algorithm What about NO 2 measurements? Do the operational wavelengths correspond to a stable point? SC routine was adapted to n2 mode.

27 Sun scan test - classical algorithm NO2, DU step # 2 steps 5% difference in NO 2

28 Sun scan test - classical algorithm NO2, DU step # 2 steps 5% difference in NO 2

29 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

30 Nonlinearity of filters F i F i + TC i TE + AF i p (1) nonlinearities in AF i p propagate to single and double ratios e.g. O 3 = 1 = 1 10 MS AFp AF p AF p AF p 6 A 1 M 2 a new routine f2 has been developed for n2 mode

31 Nonlinearity of filters o3 mode Difference relative to nominal attenuation filter pos. 1 filter pos. 2 filter pos. 3 filter pos. 4 filter pos Slit #

32 Nonlinearity of filters n2 mode Difference relative to nominal attenuation filter pos. 1 filter pos. 2 filter pos. 3 filter pos. 4 filter pos Slit #

33 Nonlinearity of filters mode filter 1 filter 2 filter 3 filter 4 filter 5 o n Error (DU) for airmass = 1 Inside the dynamic range of PMT? Filter #4 has problems... 1 classical algorithm and default NA1 value

34 Nonlinearity of filters mode filter 1 filter 2 filter 3 filter 4 filter 5 o n Error (DU) for airmass = 1 Inside the dynamic range of PMT? Filter #4 has problems... 1 classical algorithm and default NA1 value

35 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

36 Internal polarization sensitivity

37 Internal polarization sensitivity The quartz window and the grating are polarizing elements. Even unpolarized light measurements (e.g. direct sun) can be affected by the Brewer internal polarization. This is to be considered when absolute values are needed, e.g. estimate of ETCs AOD, Angstrom exponent calculations

38 Internal polarization sensitivity The quartz window and the grating are polarizing elements. Even unpolarized light measurements (e.g. direct sun) can be affected by the Brewer internal polarization. This is to be considered when absolute values are needed, e.g. estimate of ETCs This is the case! AOD, Angstrom exponent calculations

39 Internal polarization sensitivity We assume the SZA dependence to be similar for all Brewer types (also MKIV Brewers, when they operate in the visible). (A. Cede, JGR 2006) Not necessarily true, since different Brewer models use different gratings/orders (holographic grating anomalies depend on mλ/d).

40 Internal polarization sensitivity We assume the SZA dependence to be similar for all Brewer types (also MKIV Brewers, when they operate in the visible). (A. Cede, JGR 2006) Not necessarily true, since different Brewer models use different gratings/orders (holographic grating anomalies depend on mλ/d).

41 Internal polarization sensitivity Method (in field, no need of a laboratory) 1 take measurements with and without quartz window, better with fixed ND filters 2 convert to count rates, compensate for dead time, temperature and filter attenuation and forget other corrections (e.g. Rayleigh) 3 remember to convert the data back to linear units 4 calculate the ratios between measurements with/without windows interpolated at same time/airmass 5 divide them by the ratio calculated for 35 (transmittance of the QW without Fresnel effects)

42 Instrumental characterization Internal polarization sensitivity - field method

43 Internal polarization sensitivity - field method n2 mode 1 transmittance (normalized to deg.) Cede 2006 measured, slit # measured, slit #2 measured, slit #3 measured, slit #4 measured, slit # Zenith angle (deg)

44 Internal polarization sensitivity - field method o3 mode 1.1 transmittance (normalized to deg.) Cede 2006 measured, slit #1 measured, slit #2 measured, slit #3 measured, slit #4 measured, slit # Zenith angle (deg)

45 Internal polarization sensitivity - field method straylight in a single monochromator (MKIV) affects dramatically the measurements in o3 mode... and is clearly visible in n2 measurements, too

46 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

47 Temperature effect - spectral dependence year day 350 F-ratio Temperature (deg C)

48 Temperature effect - absolute values F (1e4*log10 I) slit 1 (year) slit 2 (year) slit 3 (year) slit 4 (year) slit 5 (year) slit 1 (day) slit 2 (day) slit 3 (day) slit 4 (day) slit 5 (day) Temperature (deg C)

49 Temperature effect - absolute values no detectable spectral temperature dependence slight decrease for low temperatures? Maybe just a lamp issue...

50 Effect of viewports Visible light entering through the viewports is an issue for red Brewers... and for MKIV?

51 Effect of viewports Visible light entering through the viewports is an issue for red Brewers... and for MKIV?

52 Effect of viewports ratio of corr. counts without/with cover on viewers slit #1 slit #2 slit #3 slit #4 slit # Zenith angle (deg)

53 1 Introduction 2 Overview of tests 3 Dispersion tests 4 Sun scan test 5 Nonlinearity of filters 6 Polarization sensitivity 7 Other tests 8 Conclusions and further work

54 Conclusions and further work first steps were taken towards an accurate characterization of Brewer #066 in the visible range some routines were updated for n2 mode (dsp, vi, sc, fi) however, much work remains (e.g. straylight in the visible, field of view, etc.) many thanks to Volodya, Martin, Tom and Anna Maria for their valuable help

55 Conclusions and further work first steps were taken towards an accurate characterization of Brewer #066 in the visible range some routines were updated for n2 mode (dsp, vi, sc, fi) however, much work remains (e.g. straylight in the visible, field of view, etc.) many thanks to Volodya, Martin, Tom and Anna Maria for their valuable help

56 Conclusions and further work first steps were taken towards an accurate characterization of Brewer #066 in the visible range some routines were updated for n2 mode (dsp, vi, sc, fi) however, much work remains (e.g. straylight in the visible, field of view, etc.) many thanks to Volodya, Martin, Tom and Anna Maria for their valuable help

57 Conclusions and further work first steps were taken towards an accurate characterization of Brewer #066 in the visible range some routines were updated for n2 mode (dsp, vi, sc, fi) however, much work remains (e.g. straylight in the visible, field of view, etc.) many thanks to Volodya, Martin, Tom and Anna Maria for their valuable help