Measurements Of Humidity in the Atmosphere
and Validation Experiments (MOHAVE and MOHAVE II)
Results overview
Thierry Leblanc1, Stuart McDermid1
Holger Vömel2
Dave Whiteman3, Larry Twigg3, and Tom McGee3
Larry Miloshevich4
1Jet
Propulsion Laboratory, California Institute of Technology, Wrightwood, CA. USA
2 University of Colorado, CIRES, Boulder, CO. USA
3 NASA Goddard Space Flight Center, Greenbelt, MD. USA
4 National Center for Atmospheric Research, Boulder , CO
Thanks to:
B. Demoz, G. Nedoluha, D. Venable, G. McIntyre, G. Sumnicht, K. Rush, M. Cadirola, R. Forno,
T. Manucci, C. on Ao, P. Glatefelter, M. Colgan, R. Connell, S. Oltmans, B. Johnson, J. Howe, T.
Grigsby, D. Walsh
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE : 14-28 October 2006
JPL-Table Mountain Facility, Wrightwood, Southern California
Lat. 34.5ºN
Elev. 2300 m
13.95/14 cloud-free nights during MOHAVE (annual average>320)
SRL
AT
FAKE trailers on display!
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
One example
all instruments together
- Thin layered structures well captured by all
instruments
- Very small difference between the two RS92
- Lidar profiles start getting noisy above 12 km
- RS92 dry and lidars wet with respect to CFH
Average of 4 profiles
all instruments together
- Systematic bias now clear
- Only 4 profiles including all instruments
simultaneously
- Lidar wet bias with respect to CFH
increasing with height
 Fluorescence suspected
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II
Main Result :
No more sign of fluorescence
All lidars agree well with CFH up to 12 km
1-hour lidar integration reaches in average:
- 18-19 km for ALVICE
- 15-16 km for JPL
- 13 km for AT
MOHAVEs + WAVES campaigns:
New RS92 time-lag + dry bias correction
by Larry Miloshevich, NCAR
Question:
Why does ALVICE go higher than JPL?
Answer:
Not sure (JPL gained factor 2 since the end
of the campaign but not sufficient)
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II
Another example below (JPL lidar, 10/10/2007)
Dotted: RS92 zero reference, also
time-altitude position
Solid: RS92 departure from nightly mean
Water vapor (lidar)
Departure from nightly mean
This high variability (+/-100% within 1-2 hours raises the important issue of
calibration using a non-strictly coincident measurement (e.g., radiosonde)
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II: Aura/MLS water vapor validation
Best TMF-MLS overpass shown below
Besides lack of co-location and simultaneity, and differing vertical resolution
and registration, the variability shown on JPL lidar profile within the same
night illustrates difficulty to validate satellite WV measurements
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE 2009
- Where?
JPL Table Mountain Facility
- When?
12-26 October 2009
- Who?
- 3+ water vapor Raman lidar (Leblanc/JPL, McGee/GSFC, Whiteman/GSFC)
- 15+ CFH (Vomel/DWD)
- ? NOAA Frost-Point Hygrometer (Oltmans/NOAA)
- 1+ FTIR (Toon/JPL, who else?)
- 2 Improved Microwave (Nedoluha/NRL, Kampfer/Univ. Bern)
- 50+ Vaisala RS92 PTU radiosondes (Leblanc/JPL)
- 15+ IMET PTU radiosondes (Leblanc/McDermid/JPL)
- Also ECC ozonesondes, ozone lidar, T lidar
- Also 3D transport model MIMOSA-UT/LS for cirrus and water vapor transport
MAIN OBJECTIVES:
Validation of lidar H2O above 15 km
Validation of new microwave (especially below 25 km)
Inter-comparison of FTIR, GPS and microwave TWC
Case studies of UTH transport in the vicinity of the sub-tropical jet
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOTIVATION
1. Water Vapor (WV) in UT/LS plays a major radiative role
2. WV in UT/LS variability and trends not yet well understood
3. Accurate WV measurements in the UT/LS remains very difficult
 NDACC (formerly NDSC) recently included WV Raman lidar
among its suite of long-term monitoring instruments
The MOHAVE and MOHAVE II campaigns (Oct 2006 and Oct 2007)
were designed to evaluate the current (and future)
measuring capabilities of the WV Raman lidars in the UT/LS
Each campaign involved 5 lidars, >40 PTU sondes, 10 CFH sondes, GPS,
and more…
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE
3 co-located WV Raman lidars:
AT Lidar (McGee, GSFC)
SRL temporarily “resuscitated” (Whiteman, GSFC)
JPL-TMF (Leblanc/McDermid, JPL)
49 simultaneous co-located Vaisala RS92 PTU profiles
10 simultaneous co-located ECC/CFH profiles
2 co-located GPS receivers and one WV Microwave
 >250 hours of WV lidar measurements (total)
(also 80 hours of tropospheric O3 measurements 3-27 km)
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE
Lidar characteristics (overview)
GSFC / SRL*
GSFC / AT
Laser out
355 nm
Energy/pulse
300 mJ
200 mJ
700 mJ
Rep. rate
30 Hz
50 Hz
10 Hz
Power
9W
Telescopes diam
Telescopes fov
76 cm , 25 cm
0.25 , 2.5 mrad
H2O / N2 pairs
2 x 407/387 nm
H2O filter width
0.25 nm
Other channels
2 polar. , 1 liquid
355 , 532 , 1064 nm
JPL/TMF
10 W
91 cm
1.9 mrad
1 x 407/387 nm
1 nm
4 Ram , 6 Ray
355 nm
7W
91 , 7.5 cm
0.6 , 10 mrad
3 x 407/387 nm
0.6 nm
3 Ray
* Resuscitated
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE operations
1/ Target nights: 14 nights centered to new moon
2/ New moon first priority, Aura-TMF overpasses next priority
3/ CFH : reference instrument  at least 1 CFH launch per night
(2 CFH launches on highest priority night)
4/ RS92 : 1 to 5 pairs per night, including one on same payload as CFH
5/ All lidar data analyzed for 1-hour segment following each launch
6/ MOHAVE campaign split in 2 main periods:
10/14-10/23 = mainly nominal operations (except SRL)
10/25-10/28 = Many tests related to fluorescence
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
Is this really fluorescence, as suspected?
For the JPL lidar, three tests were made on the same night:
1/ Acquire data in “normal” configuration
2/ Acquire data with additional 355 nm blocking filter
in front of optical fiber
3/ Acquire data with additional 355 nm blocking filter
immediately after the optical fiber
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
Comparisons “with” vs. “without” 355 nm block (JPL lidar)
Below (left): Presence of
fluorescence in lidar receiver
Below (right): 355 nm blocking filter inserted
at lidar receiver entrance
Not shown: Fluorescence not removed if
same block placed after fiber (not shown)
Left (bottom):
Empirical correction = 1/700 of 387 nm low-intensity
signal subtracted from H20 signal (no 355 nm signal
available in troposphere)
 when fluorescence is removed,
agreement with CFH becomes very good
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
JPL and GSFC AT lidar comparison
- No apparent systematic bias
- Only bias associated with calibration method
- RH differences peak at 2% near 10-11 km
- RH differences well below standard deviations
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
RS92 - CFH comparisons
3 datasets:
1/ RS92, no GPS
(DG 2.7 soft)
2/ RS92 w/ GPS
(DG 3.5 soft)
3/ RS92 no GPS
processed w/ 3.5
All RS92 show dry bias w.r.t. to CFH
(similar to previous Vaisala sensors)
Good repeatability of all RS92 pairs
Left: RS92-CFH
WAVES+MOHAVE campaigns + ARM site
RS92 uncorrected (far left) and
time-lag + empirically corrected (right)
by L. Miloshevich, NCAR (2008)
Courtesy of L. Miloshevich
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
LESSONS LEARNED FROM MOHAVE :
ALL 3 RAMAN LIDARS SHOWED PRESENCE OF
FLUORESCENCE IN THEIR RECEIVER
Fluorescence was not detected
in the same part of the receivers
but the same resolution came out:
ALL 3 LIDAR RECEIVERS MUST BE RE-CONFIGURED TO
SUPPRESS FLUORESCENCE
then meet again for…
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II : 6-17 October 2007
Campaign operations similar to MOHAVE
3 co-located WV Raman lidars (improved receivers)
AT Lidar (McGee, GSFC)
SRL  ALVICE (new system, Whiteman, GSFC)
JPL-TMF (Leblanc/McDermid, JPL)
41 simultaneous co-located RS92 profiles (no pairs this time)
10 simultaneous co-located ECC/CFH profiles
 240 hours of WV lidar measurements (total)
(also 80 hours of tropospheric O3 measurements 3-27 km)
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II
Lidar characteristics (overview) **
GSFC / ALVICE
GSFC / AT
Laser out
355 nm
355 , 532 , 1064 nm
Energy/pulse
350 mJ
Rep. rate
50 Hz
Power
17.5 W
Telescopes diam
60 cm
91 , 10 cm
0.2 mrad
1.9 , 4.5 mrad
Telescopes fov
H2O / N2 pairs
1 x 407/387 nm
H2O filter width
0.25 nm
Other channels
2 polar. , 1 liquid
90 mJ
50 Hz
4.5 W
2 x 407/387 nm
.25 nm
4 Ram , 7 Ray
JPL/TMF
355 nm
700 mJ
10 Hz
7W
91 , 7.5 cm
0.6 , 5 mrad
3 x 407/387 nm
0.6 nm
3 Ray
** All 3 instruments: New “fluorescence-free” Barr optics
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II
ALVICE vs. JPL :
Difference within 5-7% up to 12 km
then noise limited
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
MOHAVE II: more weather-related disturbed conditions
than MOHAVE (humidity-wise)
 high WV variability at short time scales
(two examples below from the JPL lidar)
Upper tropospheric dry
tongues penetrate into
lower troposphere
Meanwhile, humidifying
trend in the upper
troposphere throughout
the night
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
Calibration tests during MOHAVE II (JPL lidar)
Tests showed that calibration from not strictly co-located and simultaneous
radiosonde can still yield 10-15% (poor) accuracy during atmospherically
disturbed nights
To achieve 5% accuracy required for the detection of long-term
trend, an hybrid method was proposed
New hybrid method uses daily partial calibration of the lidar
receiver using a stable calibrated lamp, and a campaign-basis
absolute calibration using multiple radiosondes and the lamp
New method allows daily tracking of 2% expected or unexpected lidar receiver
changes together with long-term stability suitable for long-term
measurements
Method was described in Poster = Monday session  too late!
(contact Thierry Leblanc if interested)
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
SUMMARY
1. MOHAVE + MOHAVE II = both successful
2. MOHAVE  Fluorescence found in all three participating lidars
3. MOHAVE II  Fluorescence removed,
resulting in much better agreement with CFH in UT/LS
4. MOHAVE II  Calibration tests revealed shortfalls
of widely used calibration techniques,
Important implications for applicability to long-term measurements
5. The JPL lidar does reach expected range when compared to ALVICE
 tests are ongoing to track the cause of signal loss
6. A factor of 4 in lidar signal-to-noise ratio
should be reasonably achievable in the near-future
 When this level is achieved, water vapor Raman lidar will become a key
instrument for the long-term monitoring of water vapor in the UT/LS
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland
WHAT’S NEXT ?
A wealth of science (and validation) results is still to come
(stratospheric intrusions, simultaneous tropospheric ozone and
water vapor, total column, etc.)
MOHAVE 2009
planned for October 2009
will host more instruments: 2 microwave, 1 FTUVS, 1 FTIR, etc.
will be more science-oriented than MOHAVE and MOHAVE II
2nd ISSI Workshop on Water Vapor Instruments, 3-6 November 2008, Bern, Switzerland