Metrology meets Meteorology CITAC: 2014 Best Paper award presentation for Applied Physics B 116:883–899 (2014) Absolute validation of a diode laser hygrometer via intercomparison with the German national primary water vapor standard by B.Buchholz 1,2 , N.Böse 1 , V.Ebert 1,2 30th CITAC members meeting , 19 April 2015 1 Physikalisch‐Technische Bundesanstalt Braunschweig, Germany 2 Center of Smart Interfaces, Technische Universität Darmstadt, Germany
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Metrology meets Meteorology - CITAC · Metrology meets Meteorology ... pressure ps Pressure in the measuring cell p m ... Metrological uncertainty: 4.3% , ±3 ppmv
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Metrology meets Meteorology
CITAC: 2014 Best Paper award presentation for
Applied Physics B 116:883–899 (2014) Absolute validation of a diode laser hygrometer via
intercomparison with the German national primary water vapor standardby
B.Buchholz1,2, N.Böse1, V.Ebert1,2
30th CITAC members meeting , 19 April 2015
1Physikalisch‐Technische Bundesanstalt Braunschweig, Germany 2Center of Smart Interfaces, Technische Universität Darmstadt, Germany
Our focus: Improving atmospheric water vapor measurements
BUT:• even in static H2O lab conditions ± 10% inconsistency = “state of the art”• in airborne campaigns: local, dynamic deviations up to 30% are not unusual
Water vapor in environmental sciences/meteorology :• very important for
• atmospheric radiative balance (most important greenhouse gas)• Important correction factor for many other atmospheric sensing techniques (strongest
atmospheric constituent with the highest variability)• very important simulation parameter for climate models• atmospheric chemistry ( OH)• Cloud + aerosol formation ( phase transition water/ice) • Weather + agriculture industry • …
Field instruments: Need for pragmatic solution often far away from “metrology”• link to the SI units ?• traceability in general ?• common evaluation, calibration, interpretation strategies ? • well defined uncertainties calculations ?
WHY is there a need for improvement ?(in airborne hygrometry)
13.05.2015 5
(D. W. Fahey et al, AMTD, 2014)
e.g. AquaVIT‐I in 2008(blind comparison of world best airborne hygrometer)
Inconsistency span: 20%
B. Buchholz
reanalysis + correction of huge data sets
(e.g. MOZAIC)
13.05.2015 6
OUR philosophy
MetrologyMeteorology HOW TO LINK ?
?
Direct operation of an metrological airborne transfer standard in the field , i.e. on board of an research aircraft
13.05.2015 7B. Buchholz
STATE of development in 2011(awarded paper)
named “SEALDH – 0”
13.05.2015 8B. Buchholz
0.0 0.5 1.0 1.50.00.51.01.52.0
0.0 0.4 0.8 1.2 1.6 2.00
50100
time (ms)
dete
ctor
cur
rent
(m
A)
relative wavenumber (1/cm)
lase
r cur
rent
(mA
)
1368 1370 137220406080
100
tran
smis
sion
(%)
wavelength (nm)
H2O HITRAN SIMULATION
TDLAS PRINCIPLE
RAWSIGNAL1370 nm H2O absorption line
BASELINE-FIT
13.05.2015 9B. Buchholz
⋅⋅ ⋅ ⋅
∙ ∙ ∙ ∙ ∙Extended Lambert‐Beer‐law
with ideal gas law:measured parametersconstantsmolecular line data
E(t)
I
t
Tr(t)
calibration free! …no need for calibration procedures … just validation
DIRECT TDLAS EVALUATION
13.05.2015 10
Hygrometers andsensors under testThermostatic bath
metrology meets meteorology requirement for field applicability
13.05.2015 17
CONCLUSION
B. Buchholz
MetrologyMeteorology
Linking Metrology and Meteorology on the highest level …..while taking into account all typical airborne restrictions and requirements ‐ such as:Robustness, low maintenance, stand‐alone, high reliability, …
highly accurate and fast measurements, … airborne certification issues, ...
SEALDH‐0SEALDH‐ISEALDH‐II HAI‐IaHAI‐Ib
13.05.2015 18B. Buchholz
OUTLOOK (unpublished further validation)
All SEALDH‐II data are evaluated without any calibration !
long‐term accuracy validation at mid humidityagain at primary standards 18 month validation in three sessions
0 200 400 600 800 1000
0
1
2
3
4
5
6SEALDH-II
rela
tive
devi
atio
n (%
)(S
EA
LDH
-II -
PHG
) / P
HG
gas pressure (hPa)
600 ppmv april 2012 2500 ppmv april 2012 8000 ppmv april 2012
4 month of permanent lab-operation,
1 airborne campaign (2h), transportations, etc.
600 ppmv september 20122500 ppmv september 20128000 ppmv september 2012
23 days of permanent operation at THG
10 days operation in temperature chamber
2 airborne campaign (25h), Airtoss-I and II
12 days permanent operation at AquaVIT-II
600 ppmv november 2013
18 month time span of validationat national primary humidity standard
0 200 400 600 800 1000-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5SEALDH-II
standard deviation 0.31%
gas pressure (hPa)
600 ppmv april 2012 2500 ppmv april 2012 8000 ppmv april 2012 600 ppmv september 2012 2500 ppmv september 2012 8000 ppmv september 2012 600 ppmv november 2013