3.3
EZ Lidar™ measurement results in the frame of Nasa/Aeronet campaign Tiger-Z
Simone Lolli, LEOSPHERE, Paris, France; and L. Sauvage and F. Faijan
INTRODUCTION Lidar investigation of temporal and vertical optical atmospheric properties will play a key role in the future for a continuous monitoring over the whole planet through world ground based networks. The EZ Lidar™, manufactured by LEOSPHERE, with cross-polarization capabilities was deployed in Kanpur, India in the frame of TIGER-Z campaign organized by NASA/AERONET in order to measure aerosol microphysical and optical properties in the Gange basin. In addition, 12 sun-photometers were deployed during this campaign and CALIPSO (The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data were also acquired. In this work we present the results in retrieving aerosol extinction and backscattering from EZ Lidar™ measurements, and the validation of the space borne instrument CALIPSO under the satellite track. EZ Lidar™ is also coupled with the photometers to provide the measurements of the Aerosol Optical Depth over the selected region and the intercomparison results. MEASUREMENT SET-UP EZ Lidar™ was deployed at the Indian Institute of Technology, in Kanpur (26.8N, 80E), India, in the end of April 08. The EZ Lidar instrument was placed together with some sun photometers on the track path of the CALIPSO satellite. EZ Lidar™ uses a tripled pulse laser source Nd:YAG at 355nm wavelength with an energy of 16mJ and pulse repetition frequency of 20 Hz. Both analog and photon counting detection is available. The Lidar system provides a real time measurement with scanning capabilities of backscattering and extinction coefficients, Aerosol Optical Depth (AOD), automatic detection of the Planetary Boundary Layer (PBL) height and clouds base and top from 50m up to or more than 20 km depending on weather condition and time of the day Measurement in Kanpur took place during three days from 29th April 08 to 1st of May 08. Outside temperatures reached almost 50° C in those days. MEASUREMENT RESULTS On 29th April 08, the temporal plots of the attenuated backscattered signal showed the evolution of some altocumulus clouds at about 9 km. From the perpendicular channel, it can be detected a high presence of ice crystals inside the clouds On 30th of April, again the quick looks put in evidence in the first part the temporal evolution of some altocumulus clouds, as parallel and perpendicular channels show. Again, a high depolarization ratio in the clouds reveals a high concentration of ice crystals. In this day the global aerosol load is higher. This can be observed from the perpendicular channel that put in evidence higher depolarization values, due probably to some dust transit up to 5km. These results are in close agreement with the CALIPSO normal attenuated backscattering quick looks which show a mixing of dust and other aerosols besides the evolution of the altocumulus clouds. Further, the retrieved EZ Lidar™ Aerosol Optical Depth was validated against the in-situ sunphotometer. In order to calculate the Aerosol Optical Depth, the EZ Lidar™ integrates over the entire atmospheric column the extinction coefficient retrieved using Klett backward inversion algorithm [1]. The particle extinction is retrieved by introducing as input the Lidar Ratio [1] By default the Lidar Ratio has been set to 35 in the software. We compared AOD from the EZLIDAR and the AOD retrieved from the sun photometer located at IITK in Kanpur. We used data of April 29th 2008 from 1015 to 1258am (Local Time) and of April 30th 2008 from 0630 to 0800am (Local Time). After an iterative process, we conclude that a mean LR of 50sr on the 29th and of 90sr on the 30th is more correct for the inversion process of the Lidar data. The results of intercomparison are shown in the following Table and put in evidence a very high agreement. 29/04/2008 30/04/2008 Mean AOD sun-photometer 0.512 0.564 Mean AOD EZLIDAR 0.510 0.565 Mean Lidar Ratio (sr) 50.21 89.4 STD LR (sr) 20.39 22.28 The red curve in Figure 1 (upper) represent the AOD coefficient retrieved by the sun photometer. The white spots are the temporal evolution of the AOD retrieved by the EZ Lidar™. The retrieved total attenuated backscattering from CALIPSO satellite and EZ LIDAR™ is then compared on 29th April 08. The vertical resolution is 60m and the vertical range goes from 0 to 6km. Calipso Laser frequency is 532nm, while that of EZ Lidar™ is 355nm. The intercomparison is showed in Figure 1(Middle). The molecular backscattering wavelength dependence is well known; regarding the aerosol backscattering coefficient, the wavelength dependence is related to the Angstrom coefficient that should be measured. The difference in main level in the total attenuated backscattering coefficient is due to the strong molecular dependence. The uncertainty in the EZ total attenuated backscattering coefficient is also represented in figure 1(bottom) using equations fully developed in [3]. The intercomparison put in evidence common features of the retrieved total attenuated backscattering coefficients by EZ LIDAR™ and Calipso satellite. The difference in level is due, as told before to the different wavelength of the instruments. CONCLUSIONS The EZLIDAR instrument has been validated in the frame of TIGER-Z /NASA campaign against in-situ photometers and remote sensor as CALIPSO satellite showing a very good agreement. Outdoor and unattended use capabilities of the EZLIDAR™ (external temperatures up to 50 C) added to its measurements performances define then this instrument as a good candidate for deployment into growing global aerosol and cloud monitoring networks and research measurement campaigns. We would like to acknowledge Brent Holben and S. N. Tripathi for the sun photometer data and for the fruitful discussions regarding aerosol microphysics and dynamics over India.
Session 3, Automated Operational Lidars, Networks and Associated Studies
Tuesday, 13 January 2009, 11:30 AM-12:00 PM, Room 122A
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