Lidar and Radiosonde Measurement Campaign in Potenza for the Validation of ENVISAT Atmospheric Products

Lidar and radiosonde measurement campaign in Potenza for the validation of ENVISAT atmospheric products

G. Pappalardo, A. Amodeo, C. Cornacchia, L. Mona, M. Pandolfi, V. Cuomo lstituto di Metodologie per l’Analisi Ambientale IMAA- CNR, C.da S. Loja, Tito Scalo, Potenza, Italy, I-85050 - [email protected]

LASER: Nd :YAG laser (Coherent – Infinity) M = mirror In the frame of the validation program of ENVISAT, an intensive water vapour lidar measurement campaign, M = mirror P P = = pinhole pinhole Max. Pulse Energy @ 355nm 170mJ started on July 2002, is in progress at IMAA -CNR in Tito Scalo (PZ) (Southern Italy, 40 36’N, 15 44 ’E, 820 m M ° ° Maximum repetition rate 100Hz LL == collimationcollimation lenslens above sea level). Systematic measurements will be performed for a period of 12 months. Two measurements M Beam divergence <0.3 mrad per week have been performed for the first six months of the val idation campaign, while one measurement DM DM = = dichroicdichroic mirror mirror Pulse duration 3 ÷ 4 ns per week is scheduled for the last six months. At the moment, we have collected more than 240 hours of BS BS = = beambeam splitter splitter RECEIVING SYSTEM: Cassegrain telescope measurements. Lidar observations are complemented with radiosonde launches. PMT PMT = = photomultiplierphotomultiplier IF IF = = interferentialinterferential filter filter Primary mirror diameter 0.5 m The Raman Lidar system is based on a Nd:YAG laser equipped with third harmonic generato r (355 nm) with Combined focal length 5 m a repetition rate up to 100 Hz. The third harmonic is transmitted into the atmosphere in a coaxial mode. The Field of view 0.2 ÷ 2 mrad M receiver consists of a vertically pointing telescope in Cassegrain configuration with a 0.5 m diameter primary IF PMT mirror and a combined focal length of 5 m. The collected radiati on is split into three channels by means of 386 nm SPECTRAL SELECTION: interferential filter

dichroic mirrors. Interferential filters are used to select the elastic backscattered radiation at 355 nm, the N2 Wavelengths (nm) 386, 407 355 M Out of band rejection <10-10 <10-8 Raman shifted radiation at 386.6 nm and the water vapour Raman shifted radiation at 407 nm. Each P IF PMT nm M 386 nm Bandwidth (nm) <1.0 <1.0 wavelength is then split into 2 different channels for both low and high range signals. Photomultiplier tubes BS 355 Trasmission efficiency ~ 60% ~ 33% are used as detectors. Both low and height range signals are acquired in photon counting mode by using a IF PMT Multi Channel Scaler (MCS) with a dwell time of 100 ns. The overall characteristics of the Raman lidar are L 355 nm reported in the table. DM DETECTORS: photomultiplier IF PMT THORN EMI 9202 QB 355, 386, 407 nm M DM BS 355 nm Raman lidar measurements allow the determination of water vapour vertical profile by the simultaneous ACQUISITION: photon counting mode Nd:YAG IF PMT EG&G MCS - PCI detection of the backscattered radiation in the Raman vibrational bands of water vapour and nitrogen. Water Laser BS 407 nm Minimum dwell time 100 ns vapour Raman lidar measurements are expressed in terms of mixing ratio , that is the ratio between the mass Bandwidth 150 MHz of water vapour and the mass of dry air in a given volume. PHILLIPS SCIENT. Fast discriminator IF PMT Bandwidth 300 MHz 407 nm

WATER VAPOUR RAMAN LIDAR MEASUREMENTS

5 Semptember 2002 16 October 2002 14 October 2002 14000 14000 12000 10 Lidar (17:23 - 17:32 UT) Lidar (20:29 - 20:38 UT) Lidar (20:11 - 20:20 UT) Radiosonde (17:23 UT) Radiosonde (20:17 UT) Radiosonde (20:15 UT) 9 12000 Water vapour mixing ratio (g/kg) 12000 10000 8 10000 10000 7 DAYLIGHT CONDITIONS NIGHT –TIME CONDITIONS 8000 6 8000 8000 6000 5

6000 6000 4 Height a.s.l. (m) Height a.s.l. (m) Height a.s.l. (m) 4000 3 4000 4000

2 2000 2000 2000 1

0 0 0 0 -2 0 2 4 6 8 10 12 14 -2 0 2 4 6 8 10 12 14 -2 0 2 4 6 8 10 12 14 19:53 20:22 20:32 20:52 21:12 21:32 21:52 22:12 22:32 Water vapour mixing ratio (g/kg) Water vapour mixing ratio (g/kg) Water vapour mixing ratio (g/kg) Time (UT)

Raman lidar measurements are reported with a vertical resolution variable between 60 m and 300 m, and The false colour map shows the time evolution and vertical varia bility of water vapour mixing ratio for 14 October with an integration time of 10 minutes for both daylight and nig ht–time conditions. In the first case, the 2002. Each profile corresponds to an integration time of 5 minut es and a vertical resolution of 60 m. The map maximum height value is around 4500 m while in the second case we can retrieve water vapour profile up to shows the presence of two distinct water vapour layers that exte nd from the top of lidar station to about 2000 m 14000 m. Statistical errors for lidar water vapour measurements are within 10% up to about 4000 m of height and from 4000 m to 5500 m respectively, and that remain stable during all the acquisition time. These layers are for daylight conditions, and within 10% up to 7000 m and 25% up to 14000 m of height for night -time well evident in the reported single vertical profile obtained by integrating lidar signals in the time interval 20:11– conditions. 20:20 UT, in agreement also with the simultaneous radiosonde pro file.

MIPAS COMPARISON GOMOS COMPARISON 28 October 2002 19 September 2002

32 70 70 70 70 MIPAS (20:56:57-20:58:10 UT) MIPAS (20:57 UT) MIPAS (20:57 UT) GOMOS (10:05 UT) GOMOS (10:05 UT) Lidar (20:52-21:02 UT) Radiosonde (20:56 UT) Radiosonde (20:56 UT) Radiosonde (10:17 UT) Radiosonde (10:17 UT) 28 Lidar (20:25-23:07 UT) 60 60 60 60 Radiosonde (20:56 UT) 24 50 50 50 50

20 40 40 40 40

30 30 30 30 12 Height a.s.l. (km) Height a.s.l. (km) Height a.s.l. (km) Height a.s.l. (km) Height a.s.l. (km) 20 20 20 20 8

10 10 4 10 10

0 0 0 0 0 0 2 4 6 8 10 12 14 0 200 400 600 800 1000 200 220 240 260 280 300 0 200 400 600 800 1000 200 220 240 260 280 300 Water Vapour Mixing Ratio (g/kg) Pressure (hPa) Temperature (K) Pressure (hPa) Temperature (K) Preliminary comparisons between GOMOS and radiosonde measurements show a good agreement for both pressure and temperature profiles. However, at this stage of the validation campaign, with a small available A preliminary analysis of the comparison between MIPAS, radiosonde and lidar for water vapour mixing ratio dataset, it is difficult to draw some final conclusions; the measurement campaign at IMAA is still in progress and measurements has been performed. Water vapour lidar data can be used only for altitudes below 14 km and we’ll have more data available for comparisons in the next future. for this height region MIPAS data seem to indicate an understimation of the water vapour mixing ratio, while at higher height the agreement with radiosonde data is quite good. Improvement in the retrieval algorithm of ACKNOWLEDGEMENTACKNOWLEDGEMENT water vapour MIPAS profiles is in progress. The goal is to obtai n water vapour MIPAS profiles that extend TheThe authors authors thank thank B. B. Carli Carli and and P. P. Raspollini Raspollini(IFAC(IFAC – –CNR)CNR) for forthethe fruitful fruitful discussion discussion about aboutMIPASMIPAS products products. .

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