1. Drakkar Calibration The Drakkar microwave radiometer Calibrating Drakkar The Calibrated Data Future Work Delft, October 2004 Anne Armstrong (CETP/LMD)

2. Drakkar a microwave radiometer developed at a microwave radiometer developed atCETP sensitive to electromagnetic waves emitted sensitive to electromagnetic waves emitted at two frequencies, 23.8 and 36.5 GHz, by atmospheric water vapour and liquid water equipped with a reception antenna fixed in equipped with a reception antenna fixed in the vertical with a field of view varying from 11 to 13 degrees depending on the frequency

3. Calibrating Drakkar Using radiosounding observations, during clear-sky periods, as the input of a radiative transfer model (Kummerow), we obtained simulated Brightness Temperatures (BTs) which were then compared to the measured BTs.Using radiosounding observations, during clear-sky periods, as the input of a radiative transfer model (Kummerow), we obtained simulated Brightness Temperatures (BTs) which were then compared to the measured BTs. The Kummerow Model requires, as input,The Kummerow Model requires, as input, atmospheres including altitude, temperature & relative humidity High Resolution Radiosoundings were employed (low resolution radiosoundings and ECMWF Data were also compared)High Resolution Radiosoundings were employed (low resolution radiosoundings and ECMWF Data were also compared)

4. Calibrating Drakkar The 23.8 GHz and 36.5 GHz channels of Drakkar had been calibrated in 2001 Comparing the simulated to observed BTs during the Vapic Campaign (May-June 2004) we found the 23.8 channel to still be calibrated while the 36.5 BTs were 6 to 7 degrees too high We therefore assume the the 23.8 channel has remained calibrated during the CloudNET period In order to calibrate the 36.5 channel over the CloudNET period we assume that the Liquid Water Path should be equal to zero during periods of clear sky

5. Drakkar Products Liquid Water Path Liquid Water Path LWP = Aa + (Ab*ln(280-TB23.8)) - (Ac*ln(280-TB36.5)) Water Vapour Path Water Vapour Path WVP = Ad - (Ae*ln(280-TB23.8)) + (Af*ln(280-TB36.5)) where: Aa = 1636.36, Ab = 182.41, Ac = 476.42 Ad = 66.13, Ae = 20.72, Af = 8.99

6. LWP was summed over clear-sky periods (in January 2003) for all combinations of calibration constants varying over a range determined by comparisons made between simulated and observed BTs This plot represents the solution space of LWP C36.5=-1.8

7. LWP was summed over clear-sky periods (in July 2003) for all combinations of calibration constants varying over a range determined by comparisons made between simulated and observed BTs This plot represents the solution space of LWP Calibration validated during the Vapic Campaign (May- June, 2004) C36.5=-4.4

8. Prior to Calibration Post Calibration

9. Prior to Calibration Post Calibration

10. The Calibrated Data NetCDF files of calibrated data including brightness temperatures, liquid water path, and water vapour path are now available These files are daily starting in October of 2002 and ending mid-December of 2003 Files, which will complete the dataset (ending September 2004) will soon be available

11. Future Work Utilise the model WVP in order to refine the Drakkar calibration Intercomparison of BT calibration methods (Nicolas Gaussiat and Anne Armstrong) Automating the v&w, RadOn, and Radar-Lidar methods for the three sites Intercomparison of the CloudNET IWC Algorithms Model Evaluation with the CloudNET products