Title: LEANDRE_2 H20 DIAL Data [CNRS]

CONTACTS:

Dr. Cyrille Flamant (PI)

Institut Pierre-Simon Laplace

Service d'Aéronomie, CNRS-UPMC

4 Place Jussieu

75252 Paris Cedex 05

Voice: +33 1 44 27 48 72

Email: cyrille.flamant@aero.jussieu.fr

1.0 DATA SET OVERVIEW

The LEANDRE 2 Water Vapor DIAL system aboard the NRL P-3 was operated during the International H2O Project (IHOP_2002) field experiment from May 19 through June 25, 2002. Decription of the 24 missions performed by LEANDRE 2 during IHOP_2002 is provided in the `Summary of LEANDRE 2 operations during IHOP_2002’ also available from the JOSS web page.

2.0 INSTRUMENT DESCRIPTION

2.1 General

LEANDRE 2 is a water vapor differential absorption lidar (DIAL) developped at Service d’Aéronomie (Paris) in coopération with the Technical Division of the Institut National des Sciences de l’Univers (INSU) and was funded by the Centre National de Recherches Spatiales (CNES). This system was developped mainly to measure water vapor contents in the lower troposphere. Its broad tunability in the spectral region between 720 and 770 nm enables to reach a variety of water vapor lines with different line-strengths.

The transmitter (emitter) is a flash lamp pumped alexandrite laser that generates two closely spaced 50 mJ pulses at the absorbing and non-absorbing wavelength in the 720-770 nm spectral region. The laser beam divergence may be adjusted between 0.5 and 3.0 mrad. The spectral purity is greater than 99.99% and is controlled by a specially designed wavemeter. The receiver is a 30 cm telescope that focuses the aerosol and molecular return on an avalanche photo-diode detector which is then digitized by a dual channel (gains of 1 and 10) 12 bit A/D converter and the output of each shot is recorded on Exabyte tape. The 2048 sampling gates are separated by 15 m.

The details concerning the design of the LEANDRE 2 system and the standard DIAL signal processing are given in Bruneau et al. (2001) and only briefly presented here. The DIAL technique makes use of laser probing of the atmosphere at two wavelengths; one wavelength (so-called on-line) is centered on a water vapor absorption band and the other wavelength (so-called off-line) is positioned outside of the absorption band to act as a reference for the scattering and extinction properties of the atmosphere. The water vapor mixing ratio is determined from the difference of the slopes of the backscatter on- and off-line signals. The LEANDRE 2 system includes a tunable laser whose emission is positioned precisely upon an absorption line selected from two rotation-vibration bands in the near infrared (727-770 m). As discussed in Bruneau et al. (2001), in which the measurements errors are analyzed, LEANDRE 2 characteristics permit water vapor mixing ratio measurements to be made with a precision better than 0.5 g/kg in the 0-5 km distance (from the aircraft) range and an along-beam resolution of 300 m.

In addition to water vapor mixing ratio, simultaneous atmospheric backscatter measurements were performed at the off-line wavelength.

2.2 Operations during IHOP_2002

During IHOP_2002, LEANDRE 2 was mounted on the same aircraft as ELDORA. Not only was this the first that a Doppler radar and water vapor DIAL were flown on the same aircraft (i.e., NRL P-3), it was also the first time a water vapor DIAL was flown in horizontal-pointing mode. The operation of non-eye safe LEANDRE 2 in horizontal mode required the support of an aircraft-proximity radar and careful flight planning.

During IHOP_2002, LEANDRE 2 could be operated in a vertical pointing mode (upward and downward) as well as horizontally out of the right side of the aircraft. In order for LEANDRE 2 to operate in the vertical pointing mode, an external fairing (enclosing a turning mirror) had to be installed to deflect the LEANDRE 2 beam up or down vertically.

3.0 DATA COLLECTION AND PROCESSING

LEANDRE 2 was operated in the horizontally pointing mode during Convective Initiation (CI) and Boundary-Layer Evolution (BLE) missions. LEANDRE 2 was operated in the nadir pointing mode during Boundary-Layer Heterogeneity (BLH) and Evening Low-Level Jet (ELLJ) missions.

A total of 24 missions were completed, amounting to a collection of 142 hours of lidar data in the IHOP region:

BL Heterogeneity 7 missions 35h28

BL Evolution 3 missions 21h16

Convective Initiation 12 missions 73h18

Low-level-jet 2 missions 11h19

3.1 Quality of data

The `Summary of LEANDRE 2 operations during IHOP_2002’ details the quality of the water vapor mixing measurements for each of the 24 missions. Four categories were identified, ranging from excellent to poor.

High quality data (12 flights):

- BL Heterogeneity: 27 and 29 May; 7 June

- BL Evolution: 14 and 25 June

- Convective Initiation: 10, 11, 12, 15 and 19 June

- Low-level-jet: 7 and 20 June

These flights have been or will be processed in priority. The data from the other flights will not be processed unless one or more IHOP_2002 participants express interest in such dataset.

3.2 Data Resolution

Water vapor mixing ratio and reflectivity measurements:

- horizontal resolution (i.e. along flight track resolution) is 5 s or 10 s, which translates into 750 m or 1400 m, assuming a NRL P-3 flight speed of 140 m/s

- vertical resolution (i.e. along beam resolution) is 300 m.

4.0 DATA FORMAT AND FILE NAMING

4.1 Data format

Water vapor and reflectivity measurements are stored in the ASCII format. Each text file begins with a header including aircraft and lidar specific data. Missing data are marked by "-9999." Or reflectivity and "NaN" for water vapor mixing ratio. They can be caused by optically thick clouds leading to strong absorption of the backscatter signal, or detector saturation due to strong backscatter.

Each flight is composed of a number of legs. For a given leg, a number of water vapor and reflectivity profiles (5 or 10 s resolution) are provided (in a unique data file). As an example, flights are generally composed of 10 to 20 legs, each leg totalling between 50 and 100 profiles.

Importantly, the format of the LEANDRE 2 data is not the same for data collected in the horizontal pointing mode (CI and BLE missions) and vertically pointing mode (BLH and ELLJ).

4.1.1 Horizontally pointing data format

The lidar derived water vapor mixing ratio and reflectivity profiles are fully navigated (i.e. an altitude, latitude and longitude is associated with each range-resolved water vapor and reflectivity value). The data is organized in 6 columns as shown below.

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4.2 File Naming Conventions

One data file is provided for each mission (L2_ddmmyy_all.tar) which contains data from all the legs performed during the flight (L2_ddmmyy_leg*.tar.gz). Each legs is composed of individual profile named LWyyyymmdd.hhmmss.XXX, with

YY=year, MM=month, DD=day, HH=hour, MM=minute, SS=second

5.0 LEANDRE 2 H2O-DIAL IHOP_2002 data set release history

First release (31 August 2004)

CI missions: 10, 11, 12 and 19 June 2002

22 May 2002

10 June 2002: 13 legs contained in one file (L2_100602_all.tar)

10 s resolution data

L2_100602_leg1.tar.gz

L2_100602_leg2.tar.gz

L2_100602_leg3.tar.gz

L2_100602_leg4.tar.gz

L2_100602_leg5.tar.gz

L2_100602_leg6.tar.gz

L2_100602_leg7.tar.gz

L2_100602_leg8.tar.gz

L2_100602_leg9.tar.gz

L2_100602_leg10.tar.gz

L2_100602_leg11.tar.gz

L2_100602_leg12.tar.gz

L2_100602_leg13.tar.gz

11 June 2002: 15 legs contained in one file (L2_110602_all.tar)

10 s resolution data

L2_110602_leg1.tar.gz

L2_110602_leg2.tar.gz

L2_110602_leg3.tar.gz

L2_110602_leg4.tar.gz

L2_110602_leg5.tar.gz

L2_110602_leg6.tar.gz

L2_110602_leg7.tar.gz

L2_110602_leg8.tar.gz

L2_110602_leg9.tar.gz

L2_110602_leg10.tar.gz

L2_110602_leg11.tar.gz

L2_110602_leg12.tar.gz

L2_110602_leg13.tar.gz

L2_110602_leg15.tar.gz

12 June 2002: 22 legs contained in one file (L2_120602_all.tar)

10 s resolution data

L2_120602_leg1.tar.gz

L2_120602_leg2.tar.gz

L2_120602_leg3.tar.gz

L2_120602_leg4.tar.gz

L2_120602_leg5.tar.gz

L2_120602_leg6.tar.gz

L2_120602_leg7.tar.gz

L2_120602_leg9.tar.gz

L2_120602_leg10.tar.gz

L2_120602_leg11.tar.gz

L2_120602_leg12.tar.gz

L2_120602_leg13.tar.gz

L2_120602_leg14.tar.gz

L2_120602_leg15.tar.gz

L2_120602_leg16.tar.gz

L2_120602_leg17.tar.gz

L2_120602_leg18.tar.gz

L2_120602_leg19.tar.gz

L2_120602_leg20.tar.gz

L2_120602_leg21.tar.gz

L2_120602_leg22.tar.gz

19 June 2002: 20 legs contained in one file (L2_190602_all.tar)

10 s resolution data

L2_190602_leg1.tar.gz

L2_190602_leg2.tar.gz

L2_190602_leg3.tar.gz

L2_190602_leg4.tar.gz

L2_190602_leg5.tar.gz

L2_190602_leg6.tar.gz

L2_190602_leg7.tar.gz

L2_190602_leg8.tar.gz

L2_190602_leg9.tar.gz

L2_190602_leg10.tar.gz

L2_190602_leg11.tar.gz

L2_190602_leg12.tar.gz

L2_190602_leg13.tar.gz

L2_190602_leg14.tar.gz

L2_190602_leg15.tar.gz

L2_190602_leg16.tar.gz

L2_190602_leg17.tar.gz

L2_190602_leg18.tar.gz

L2_190602_leg19.tar.gz

L2_190602_leg20.tar.gz

22 May 2002: 13 legs contained in one file (L2_220502_all.tar)

5 s resolution data

L2_220502_leg1.tar.gz

L2_220502_leg2.tar.gz

L2_220502_leg3.tar.gz

L2_220502_leg4.tar.gz

L2_220502_leg5.tar.gz

Upcoming releases (31 September 2004)

CI missions: 9 and 15 June 2002 (31 September 2004)

ELLJ mission: 20 June 2002 (31 December 2004)

BLH missions: 27 and 29 June 2002 (31 December 2004)

6.0 REFERENCES

Bruneau, D., P. Quaglia, C. Flamant, M. Meissonnier, and J. Pelon, 2001: Airborne lidar LEANDRE II for water-vapor profiling in the troposphere. Applied Optics, 40, 3450-3475.