Tropospheric Ozone Lidar Upgrade and Automation at JPL Table Mountain Facility

As part of the international efforts to monitor the global ozone concentration, different satellite missions were deployed (e.g. TROPOMI) and others, like TEMPO, are planned for the near future. Considering the importance of the validation stage of these missions, two main modifications were introduced on the Jet Propulsion Laboratory Table Mountain Facility (JPL TMF) tropospheric ozone lidar (TMTOL) to provide accurate and extensive datasets for this purpose.

The first major modification consists on the full automation of the lidar system, which is now capable of measuring untended during satellite overpasses. The system automation hardware was implemented in a modular approach to ease its migration to other TMF lidar systems (stratospheric ozone and Raman water vapor lidars). Communication between subsystems is carried out via Ethernet interface, while the power of each subsystem is controlled with an Ethernet controlled Power Distribution Unit (PDU). Since there is no window protecting the lidar from precipitation, a hardware interlock was implemented to ensure that in case of precipitation and hardware failure, the protective hatch automatically close.

The control software is implemented in Python, with a web-browser-based user interface implemented with Bokeh library. The control software is divided in five different modules: a web interface that allows the programming of the system and the monitoring of its status, a scheduler that deliver the program commands to the rest of the modules, a housekeeping module that controls most of the lidar hardware, an alignment module that performs alignment on the receivers before each measurement period and an acquisition module that stores the measurements together with system status data and meteorological data to help to interpret measurements and help on the debugging of possible problems.

The second modification consists of a novel very-near-range receiver developed to reduce the minimum achievable range of the tropospheric ozone lidar down to about 100 m AGL. While the other TMTOL receivers are based on the 289/299 nm wavelength pair generated by frequency shift from 266 nm by two Raman cells, the new receiver is based on the 266/289 nm wavelength pair transmitted from one of the Raman cells used on this system. The use of the output of one of the cells minimizes the overlap difference between both receiver arms. Additionally, the wavelength pair used for this receiver minimizes the aerosol contamination on the DIAL retrieval process. Atmospheric backscatter is then collected by a 2-inch lens and divided in two beams by a pellicle beam splitter (BS) which also minimizes the overlap difference between both arms of the receiver. Interference filters (IFs) filter out solar background light and the reciprocal DIAL wavelength before being detected by the photomultipliers (PMTs).

As part of the validation procedure for this new very-near-range receiver, a set of measurements with a balloon-borne ozonesonde as well as long-term comparison with a surface ozone meter were conducted. The comparison with the ozonesonde shows a very good agreement down to 100 m AGL (see attached figure), while long-term comparison with the surface ozone measurements show good agreement when considering the separation between first valid lidar-retrieved bin and surface concentration. Further validation is expected to be performed soon by means of a small ozone sensor mounted on an unmanned aerial vehicle. This would not only provide extensive datasets for the validation of the very-near-range receiver but also means to quantify near ozone variability.