Transcript DRL DIAL (Kiemle)

High Resolution Airborne DIAL Measurements of Water
Vapor and Vertical Humidity Fluxes during IHOP
Christoph Kiemle, G. Ehret, A. Fix, H. Flentje, G. Poberaj, M. Wirth (DLR)
R. M. Hardesty, W. A. Brewer, S. P. Sandberg (NOAA)
IHOP Water Vapor Intercomparison Workshop, Boulder, 2.10.2003
Overview
• Differential-Absorption-Lidar (DIAL) in the DLR Falcon aircraft
• High resolution water vapour measurements of the boundary layer
• Evaluation of systematic and statistical uncertainties
• Co-located wind lidar measurements and vertical humidity fluxes
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IHOP Objectives and DIAL Performance
IHOP 2002
missions
Objectives
Falcon
flights
BL
heterogeneity
Improve understanding of the relationship
between atmospheric water vapor,
surface fluxes and boundary layer
processes as they relate to quantitative
forecasts of precipitation
11
10:21
25:57
39,9
2
2:29
5:09
48,1
understand and predict the processes
that determine where and when
convection forms
3
3:19
9:32
34,8
Low level jet
5
4:34
10:43
42,7
TOTAL
21
20:43
51:21
40,4
BL evolution
Convection
Initiation
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H2O aerosol H2O /
data
data aerosol
(hh:mm) (hh:mm) in %
On board the DLR Falcon
H2O DIAL: Telescope, detectors
and passive cooling unit
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H2O DIAL: Operators’ seat
with quick-look display
DIAL System Parameters and Set-up
Wavelength
(nm)
927
1064
532
Pulse
energy (mJ)
12
50
40
Repetition
rate (Hz)
50
(on/off)
100
100
Pulse
length (ns)
7
15
11
Bandwidth
(GHz)
0.14 / 90
0.05
0.05
Si:APD
Si:APD
(s&p pol)
PMT
(s&p pol)
Filter
FW HM (nm)
1
1
1
Filter trans.
(%)
65
40
55
Detector
Telescope
Cassegrain, Ø35 cm
field-of-view: 1 - 2 mrad
Data
acquisition
14 bit, 10 MHz
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Falcon payload during IHOP_2002
u,v,w,TAS
T,P,q
Dropsondes:
u,v, P,T,q
DIAL:
u,v
HRDL:
W'
H2O, Aerosols
Horizontal & vertical wind speed
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High Resolution Backscatter and Water Vapour Cross Section
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H2O data:
73
hor. res., 100 m vert. res. in near range, 300 m in far range; overall stat. error 7%
Physik
derm
Atmosphäre
Water Vapour Spectra and Variance Profile
energy spectra of horizontal water vapor series at 2450m asl.
2
(g/kg)
energy spectra of horizontal water vapor series at 1820m asl.
0.1
0.1
(g/kg)
2
0.01
0.01
0.001
0.001
0.0001
0.0001
10000
wavelength [m]
1000
10000
wavelength [m]
1000
km asl.
3.0
2.5
2.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
water vapor variance profile (g/kg) 2
uncorr. stat. err. variance (dashed)
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Method for Estimating the Statistical (Random) Error
autocovariance of horizontal water vapor series at 1820m asl.
IHOP, 7 June 2002, 17:39 - 17:46:30 UTC
2
(g/kg)
3.5
Mean of 450 profiles with zeff = 100 m, x = 146 m
(Reference = High resolutions )
Mean of 450 profiles with zeff = 150 m, x = 146 m
(Low vertical resolution)
Mean of 225 profiles with zeff = 100 m, x = 292 m
(Low horizontal resolution )
0.6
σ2q,instr.
Height a.s.l., km
3.0
0.4
σ2q, atmos.
0.2
2.5
2.0
0.0
1.5
-0.2
1.0
-2000
-1000
0
1000
lag [m]
RMS error 
q
q
2000

3000
0
10
20
30
Rel. Stat. Uncert. of Water vapor Mixing Ratio (RMS), %
 noise
q
q
q
Assumption: hor. homogeneity
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4000
 x 
1 2
z 3 2
DIAL resolution scaling law
Discussion of Systematic Uncertainties
IHOP, 7 June 2002, 17:39 - 17:46:30 UTC
IHOP, 7 June 2002, 17:39 - 17:46:30 UTC
3.5
3.5
Height a.s.l., km
3.0
2.5
-3 hPa
+3 hPa
-2 K
+2 K
BSR1
SP = 96 %
SP = 94 %
3.0
Height a.s.l., km
SP = 96 %
SP = 95 %
SP = 94 %
Dropsonde
2.0
1.5
-3 hPa
+3 hPa
-2 K
+2 K
BSR1
2.5
2.0
1.5
1.0
3
4
5
6
7
Water vapor Mixing Ratio, g/kg
Reference profile (SP=95%) with
dropsonde and “worst case”
systematic deviations
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8
1.0
-5
-4
-3
-2
-1
0
1
2
Difference to SP95, %
3
4
5
Summary of DIAL Uncertainties for IHOP 2002
Error source
Worst case
uncertainty
Maximum H2O
rel. uncertainty
Comments
Remedy
TBD
TBD
Line-dependent,
significant
Accurate line parameter
measurement
TBD using
simulation
model
<1%
(Ismail & Browell,
1989)
 3 hPa
<  0.5 %
Small
Atm. temperature
2K
4%
Significant
Use temp. indep. line
Spectral purity
1%
Range-dependent,
significant
Laser SP > 99 %, more
stable conditions
H2O absorption
cross-section
Rayleigh Doppler
effect
Atm. pressure
Dependent on aerosol Use correction scheme
and water vapour
based on temperature
gradients
and aerosol backscatter
Near
range
Far
range
1%
4%
Total systematic uncertainty
without absorption crosssection uncertainty
4.3 %
5.8 %
Geometrically added:
errors are assumed to
be “random”
Estimated statistical uncertainty for
horizontal and vertical resolutions
of ~1.5 km (10 s) and 200 m
0.5 %
3.4 %
Dependent on range,
background light,
laser power, etc.
Overall uncertainty (preliminary)
4.8 %
9.2 %
Algebraically added
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H2O DIAL Comparisons with Dropsondes
5
H2O DIAL
Dropsonde
Altitude [km]
4
June 9, 2002, 12:51 UT
3
100.21W, 36.56N
2
Altitude [km]
5
H2O DIAL
Dropsonde
June 9, 2002, 13:17 UT
4
3
102.71W, 36.55N
2
1
6
8
10
12
H2O Mixing Ratio [g/kg]
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14
1
2
4
6
8
10
12
H2O Mixing Ratio [g/kg]
14
High Resolution Water Vapor and Vertical Wind
height (km)
DLR DIAL water vapour mixing ratio
3.0
DLR-DIAL:
3.0
2.5
2.5
2.0
2.0
x = 150 m
y
1.5
1.0
1.5
1.0
-101.92
-101.90
-101.88
-101.86
longitude
-101.84
= 150 m
-101.82
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
g/kg
height (km)
NOAA HRDL vertical wind velocity
3.5
3.0
2.5
2.0
1.5
3.5
NOAA-HRDL:
3.0
x = 150 m
2.5
2.0
y = 150 m
1.5
0
2
4
6
8
10
distance (km)
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-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
m/s
Co-located Airborne Water Vapour and Wind Lidars
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Estimation of Latent Heat Flux Profile by Eddy Correlation
Flux F = w’q’
q’ = q - q
statistical error (solid):
σ2F, instr. = Δt/T σ2w atm. σ2q, instr.
Ritter et al., JGR, 1990
sampling error (dashed):
σ2F, sampling =
2 ISF/T (F2 + σ2w atm. σ2q, atm.)
Lenschow and Stankov, JAS, 1986
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