2DC

FAAM CORE 2 Dimensional Particle Size Spectrometer

2DC is a two dimensional particle size spectrometer manufactured by Particle Measuring Systems. It fulfills the core data-set requirement for water droplet and ice crystal size spectra ranging from 50µm to 800µm diameter. The probe is a wing mounted instrument which houses a HeNe laser and a photodiode array and detection system. It is operated as part of the Core Cloud Physics Console. The core data product is a 5-second averaged values of:

2DC

particle number concentration
particle diameter
condensed water content
mean volume radius
precipitation rate and size spectrum

Particle diameter is determined from the shadow image using a single defined algorithm. This is the mean of maximum dimensions measured parallel and perpendicular to the detector array. The dimension perpendicular to the detector array is corrected for differences between the actual aircraft true airspeed and that used to set the probe clock rate. Condensed water content and precipitation rate are determined by calculating individual particle masses and fallspeeds using specified functions of the particle diameter. There is an option to specify that the particle images are to be treated as either all ice or all liquid.

System components

2DC's basic components and theory of operation is as follows:

A class 3a HeNe laser is directed across 2DCs two extension arm ends by two 45° mirrors housed inside the extension tip ends. This produces a sample area through which the air sample flows.
When a particle crosses the beam, a shadowgraph is produced. The leading edge of this shadow image is detected on a linear array of photodiodes. Signals are recorded (successive 32 bit wide slices in RAM chips) until the particle leaves the sampling area, when a time stamp is recorded. The relative strength of the scattered light in the detector determines the particle size.
This data is stored in the memory until full. A second memory then takes over whilst the first memory 'unloads' to the data acquisition unit.
This information is streamed to the onboard SEADAS computer, where the data is stored and images are displayed in real-time.

Instrument specifications:

Size range	25µm to 800µm
Number of bins	32
Particle size resolution	32 x 1024 bits
Sampling frequency	5 hz average
Maximum particle velocity	125 knots
Laser wavelength	632 nm
Temperature	-60 to +50 degrees C
Altitude	0 - 60,000 feet MSL

2DC extension arms Rigorous cleaning, laser alignment and maintenance regimes continue at FAAM laboratories which ensures 2DC continues to produce high quality and dependable data for use in the scientific community.

Documentation

All manuals and procedure documents are available from FAAM (contact details below).

Further details

Contact Angela Dean