Back-scatter Cloud Probe with Polarization Detection

The BCPD measures cloud droplet size distributions, which are then used to derive the total number concentrations, liquid water content (LWC), median volume diameter (MVD), and effective diameter (ED). The BCPD’s non-intrusive optical housing allows use in a range of ground-based or airborne applications with no contamination from ice crystal shattering and no airflow distortion.


Discriminate between ice and water particles with the BCPD’s polarization feature. For example, use the BCPD to detect when an aircraft encounters abnormally high concentrations of ice crystals.

Minimize airflow disturbance and enable undisturbed particle measurement with the BCPD’s aerodynamic design. Mount the BCPD easily on aircraft, even when space is at a premium.

Monitor multiple output variables like total particles, average transit time, over-range particles, and various probe health indicators. Get particle classification by size in histogram form.

Depend on automatic correction for drifts in polarization signals through the dynamic thresholding feature.

Program the instrument's sample rate and size bin thresholds. Plus, get size distributions accumulated in the probe, with serial transmission to a computer via any standard RS-422 communications port.

Particle light detection and polarization detection

  • Particles passing through the laser beam scatter light in all directions.
  • Some of this light is transmitted within a cone with subtending angles between 143° and 169° (156° ± 13°). These photons are directed onto a photodetector that converts their photon pulses into electrical pulses, which are then transmitted to a signal processor that amplifies and digitizes them.
  • Mie theory is used to determine the particle’s size from the peak amplitude of the scattering signal. At programmable intervals, the BCPD sends out a particle size distribution. This information is then used to determine particle number concentration.
  • A beam splitter separates P-polarized from S-polarized light, and a comparison of the components allows separation of water droplets from ice crystals.
Measured Parameters Single-particle light scattering:
  • S polarized back-scattered light
  • P polarized back-scattered light
Auxiliary Parameters
  • Temperature
  • Pressure
Derived Parameters
  • Particle diameter
  • Particle number concentration
  • Liquid water content (LWC)
  • Effective Diameter (ED)
  • Median volume diameter (MVD)
Particle Size Range 2 - 50 µm
Number of Size Bins
  • 10, 20, 30, or 40 (configured at time of purchase)
  • User-selected boundaries
Number of Concentration Range 0 - 1,000 particles/cm3
Air Speed Range 10 - 250 m/sec
Sampling Frequency Selectable, .04 sec to 20 sec
Light Collection Angles Center-line: 155°, +/- 18.5°
Laser 658 nm
Laser Power 85 mW or less
Data System Interface RS-422 serial interface
Environmental Operating Conditions
  • Temperature: -40° to 40°C
  • Relative Humidity: 0 - 100%, non-condensing
  • Altitude: 0 - 50,000 feet (0 - 15,000 meters)
  • 1.4 kg for head and window interface
  • 0.9 kg for electronics box
Probe Dimensions
  • Probe alone: 14.7 cm L x 13.3 cm W x 6.4 cm H
  • With window interface: 16.7 cm L x 13.3 W x 8.3 cm H
Electronic Box Dimensions 21.6 L cm x 12 cm W x 8.2 cm H
Power Requirements 28 VDC, 5 A for system and heaters

The Lifecycle Care Program ensures BCPD integrity and performance vital to your research mission for 3 years or 3 calls (whichever comes first). When conducting complex and time intensive laboratory or field measurements it is critical to avoid down time, and ensure data collection accuracy. The program consists of 3 key deliverables for each year or call:

  • Instrument Logistics
  • Instrument Integrity
  • Instrument Performance

Lifecycle Care Program Includes:


  • Shipping to and from Droplet Measurement Technologies facility
  • Customs handling, including CARNET ATA if required


  • Incoming instrument evaluation and health check


  • Software and firmware validation
  • 100%-unit functionality test
  • Calibration data
  • Calibration report
  • Certificate of calibration

At times, our technician might discover an instrument issue, which might not be covered by the Lifecycle Care Program or by our product warranty. In such case we will reach out to you with a service & repair estimate to allow you to provide us with the next steps of action.