N EW C APABILITY FOR O ZONE DIAL P ROFILING M EASUREMENTS IN THE T ROPOSPHERE AND L OWER S TRATOSPHERE FROM A IRCRAFT

Recently, we successfully demonstrated a new compact and robust ozone DIAL lidar for smaller aircraft such as the NASA B200 and the ER-2 high-altitude aircraft. This is the first NASA airborne lidar to incorporate advanced solid-state lasers to produce the required power at the required ultraviolet wavelengths, and is compact and robust enough to operate nearly autonomously on the high-altitude ER-2 aircraft. This technology development resulted in the first new NASA airborne ozone DIAL instrument in more than 15 years. The combined ozone, aerosol, and clouds measurements provide valuable information on the chemistry, radiation, and dynamics of the atmosphere. In particular, from the ER-2 it offers a unique capability to study the upper troposphere and lower stratosphere.


INTRODUCTION
NASA Langley's current airborne lidar Ozone and Aerosol Lidar instrument provide profiles of ozone via the Differential Absorption Lidar (DIAL) technique and aerosol and cloud optical properties via the High Spectral Resolution Lidar (HSRL) technique. This lidar has been a much relied-upon facility-class instrument for deployment on the larger aircraft platforms (i.e., DC-8) over the last three decades, having been deployed on 33 major field experiments focused on investigation of regional-and global-scale processes within tropospheric and stratospheric, satellite validation, and model assessments [1]. Ozone lidar measurements continue to be a requirement on many NASA-sponsored airborne process studies and validation campaigns such as the recent and successful SEAC4RS and KORUS campaigns and will be important for future satellite (e.g. TEMPO and SAGE-ISS) validation campaigns.
This abstract provides a technical overview of major subsystems of this new instrument, an overview of potential new investigations, and highlight a few examples of ozone and aerosol profiles acquired during flights in January 2016 and April 2016 from the B200 and ER-2 aircraft platforms, respectively. In addition, the ozone profiles measured by the lidar are compared with profiles from ozonesondes and ground-based TOLNet ozone lidar systems.

METHODOLOGY
This new system is designed to combine aerosol/cloud and the trace gas ozone measurements into a single integrated instrument. The driving requirement was to develop a lidar system that is much smaller, lighter, and uses less power compared to previous generations. In addition, to fly on the ER-2 aircraft the system had to operate autonomously or with very limited remote control.

Laser Subsystem
A critical development was the laser systems. mixed with 355nm in two SFG crystals to produce the 290nm and 300nm ozone DIAL wavelengths.

Receiver Subsystem
The receiver consists of multiple channels for the aerosol/cloud and ozone measurements. The system incorporates the HSRL technique at both 532nm and 355nm using an iodine vapor filter and Michelson Interferometer, respectively. The 1064nm channels are detected using the standard backscatter approach with calibration from the 532nm channel.
The 532nm and 1064nm retrievals are implemented similar to Hair et al. (2010) [2]. The system also measures the linear depolarization ratio for all three wavelengths [3]. The system has flown on multiple campaigns with the aerosol/cloud measurement channels since 2012. Here we report additional channels that are included in the system to enable ozone profiling through the Differential Absorption Lidar (DIAL) technique focused on measurements in the lower stratosphere and troposphere.
These ozone wavelengths are transmitted simultaneously and are split in the receiver with a dichroic filter where each channel has 1nm wide interference filter before the photomultiplier detectors.

Overall System Design
As noted above, a main objective was to reduce the overall size, weight, and power requirements of this new instrument compared to the current airborne ozone DIAL system that Langley has flown over the past 3 decades.
This was accomplished mainly by the laser system approach and design along with the supporting custom electronics and chillers. In addition, considerable effort was put forth in the design of the receiver and instrument structure.
The telescope incorporates a 40cm diameter all-metal telescope and a dual-sided aft-optics breadboard. A comparison of the two system sizes is provided in Figure 2 and Table 2. The new system is configured to view downward (e.g. from ER-2) in contrast to the current DIAL system, which simultaneously views in the nadir and zenith directions (e.g. from DC-8).    large-scale dynamics related to convection in the tropics and the Brewer-Dobson circulation.

CONCLUSIONS
The first NASA airborne ozone lidar developed to fly on both small aircraft (B-200) and highaltitude aircraft (ER-2) has successfully demonstrated. The instrument performed well on all the 12 flights conducted to date and demonstrated reliable and hands-off performance of dual OPO-based UV lasers at 290nm and 300nm. These flights provided the first opportunity to assess the measurement performance. The lidar ozone profiles compared well with profiles from coincident ozonesonde launches to within 1.2% with a variation of 5.7% on average. The airborne lidar profiles also compared well with profiles from the groundbased TOLNet DIAL lidar at University of Alabama in Huntsville. Comparisons to the other TOLNet sites have yet to be analyzed. The flights from the ER-2 demonstrated the lidar performance in a near autonomous operation and provided unique profiles of the lower stratosphere and upper troposphere ozone and aerosol distributions. In addition, current plans are to implement a recently developed Fibertek Inc. OPO laser system that operates at 304 and 316nm. This laser system is currently being integrated with the same pump laser described above and will enable profiling from 20km to the surface at all latitudes.