TITLE: Twin Otter Particle size distributions as measured by the FSSP-100 probe. Submitted 17 Dec 2002 Version 1.0 AUTHOR: Haflidi H Jonsson CIRPAS/Naval Postgraduate School 3240 Imjin Road, Hangar 510 Marina Municipal Airport Marina, CA 93933 Tel: 831-384-2776 Fax: 831-384-3277 e-mail: hjonsson@nps.navy.mil 1.0 DATASET OVERVIEW The dataset contains the location, as well as per channel concentration of particles for the 20 fssp channels. Particle diameters are given as geometric mean diameters for each channel. Probe response is calculated for various refractive indexes likely to be present in the atmosphere (1.33 <= RI <= 1.7). The curve cluster is lined up on calibration data. The cluster of curves thus defines the envelope of possible particle sizes that could generate the measured pulse. An upper and lower envelope diameter value is thus determined for each channel boundary. Reported with the data are channel diameter based on the geometric mean boundary diameters. The envelope values, which define the uncertainty in the inversion are not presented in the data file. If interested in discussing them, please contact the POC above. 2.0 INSTRUMENT OVERVIEW The FSSP-100 probe collects light scattered through a 4-14 degree angle out of a laser beam in the forward direction. The resultant pulse gererated by the photodetectors are classified by height into 20 channels, resulting in a pulse height spectrum every second. The probe is calibrated by use of monodisperse spherical polystyrine and glass spheres, and the resultant mean pulse heights combined with calculated probe response used to generate an inversion scheme that converts measured pulse height spectra to size distributions. The FSSP-100 has four gain ranges that determine the dynamic range of the probe. In this experiment the probe was operated in gain range 2, which covers particle diameters from approximatyely 0.8 to 16 micrometers. 3.0 DATA COLLECTION AND PROCESSING Data were logged to the CIRPAS Twin Otter data system, which is based on National Instruments computers and LabView instrument drivers. The CPAS probe is polled for its pulse height spectra once every second.