Weather Station and LIDARUpgrades at PEARL

Mathilde Jutras1, A. Tikhomirov1, and J. R. Drummond11 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada

IntroductionThe laser of the Arctic Ozone DIAL failed in March 2009 and was replaced by one with a new pulse rate of 200 ns, requiring some changes in the equipment. Most of all, the chopper, preventing detector's saturation from the scattering in the lower atmosphere, needs to be changed for one with a different, very precise, rotation speed. To maintain the wanted speed, a PID loop controller is required to constantly adjust the speed.

On a different subject, two new weather stations have been installed in Eureka, NU, providing interesting information about local effects of the weather.

LidarA lidar is an instrument that is used to retrieve information about different components of the atmosphere. The name stands for '' Light Detection And Ranging''. Light from a laser is transmitted in the atmosphere and the scattered light is gathered by a telescope and sent to photomultiplier detectors through different channels measuring different wavelengths. [1]

The Arctic Ozone DIAL A DIAL is a lidar sending two wavelengths: one in the high intensity peak of the spectrum of the particle we are measuring and one out or it. Comparing the two wavelengths and knowing the speed of light, we can retrieve the concentration profile. Auto-calibration Pulse rate of 200 ns λ

on = 308 nm, λout = 353 nm [2]

Figure 1 : schematic figure of a lidar. Source : WEITKAMP, Claus. Lidar. Range-Resolved Optical Remote Sensing of the

Atmosphere. Springer, 2005.

ChopperThere is a lot of scattering in the atmosphere at altitudes of less than 10 km and the signal coming from this part of the atmosphere must not reach the detectors. That's because the detectors operate in the photon-counting mode and are very sensitive, so they would saturate easily. Therefore, we need a rotating blade (chopper) that blocks those photons and lets the ones from the upper atmosphere enter the system.

Fast transition from closed to open Speed limited by the motor 4 blades, 9000 rpm, using 1 out of 3 pulses

The chopper is in conjuction with the laserto ensure proper trigger timing.

PID Controller

Proportional: current error

Integral: accumulation of past errors, accelerates toward setpoint

Derivative: rate of change of the error, stabilisation

Conclusion & Future Work The DIAL system's chopper along with the PID controller should avoid saturating the detectors.

The chopper will be installed on the Ozone DIAL system in Eureka and the lidar will hopefully be operative again for winter 2013-2014

The new weather stations will provide more information on vertical wind variations around the Ridge Laboratory

They will also show how the weather at sealevel is different from the weather at the Ridge laboratory.

References [1] G. J. NOTT et al. A Remotely Operated Lidar for Aerosol, Temperature, and Water Vapor Profiling in the High Arctic (2011) [2] Optech Incorporated, Arctic Ozone DIAL system, User Manual (1993)

AcknowledgmentThe author would like to thank NSERC CREATE which provided the funding and CANDAC for theequipment and installations.

OPAL

Weather in EurekaNewly installed weather stations in Eureka

New weather station

Old weather station

Confirmation of the data given by the old weather station Difference between the Ridge lab and OPAL At the Ridge lab, difference between the ground and the roof

OPALRIDGE LAB

Eureka80°N, 86°25'W

For more information, contact Mathilde Jutras at mathilde.jutras@umontreal.ca

Optical sensor

Blade

Motor

The data are retreived and treated by programs written in the python programming language

Observations :● Some wind episodes are different at the Safe Hut and at the Ridge Lab ("Pearl")● Higher temperatures at OPAL (summer, sea level)