Cloud Particle Spectrometer with Polarization Detection (CPSPD)



A state-of-the-art probe that measures cloud droplets, ice crystals, volcanic ash and other airborne particles in the .65 to 30 µm range.
Special Features: Particle-by-particle data (optional)



  • Cloud studies
  • Ice crystal studies
  • Aerosol-cloud interaction research 
  • Volcano emissions research

Photo at right: The CPSPD mounted on the SAFIRE Falcon 20.

CPSPD on SAFIRE Falcon 20



  • Provides valuable insight into particle shape and composition
  • Offers particle-by-particle data 
  • Allows open-path, in-situ measurements
  • Features anti-shatter tips for accurate counting and sizing
  • Records extensive data on system operating conditions to ensure optimum performance
  • Allows user to select sampling rate
  • Reduces particle coincidence issues by measuring scattering off of laser axis



Optional Feature: Particle-by-Particle Feature (PBP) Data

PBP data provide precise information on particle scattering intensity and inter-arrival times. PBP data are useful when investigating small-scale cloud structure to identify mixing and entrainment, drop breakup and coalescence, and micro-scale turbulence. PBP data also give the most accurate per-particle polarization information.



The Particle Analysis and Display System (PADS, right) is optional software that provides a user-friendly virtual instrument panel.

PADS allows the user to control the CPSPD and display real-time data and logs. For instance, the program enables the user to do the following tasks: 

  • Sample and record data 
  • View particle volume and number concentrations, as well as Median Volume Diameter (MVD) and Effective Diameter (ED)
  • Monitor instrument parameters like CPSPD laser current and various electronics voltages
  • Play back data for post-flight viewing
  • Reprocess data with new parameters for additional analysis


How It Works

The CPSPD measures three components of light scattered by cloud and aerosol particles that pass through a focused laser beam: forward-scattered light and parallel and perpendicularly polarized back-scattered light. Separate optical systems collect and direct the light onto individual detectors. 

Particle size is inferred from the intensity of the forward-scattered light, while a particle’s deviation from a spherical shape is derived from the comparison of the two components of back-scattered light. The refractive index of spherical particles is estimated from the relationship between the forward and back-scattered light (Baumgardner et al., 1996).



Parameter Specification
Measured Parameters Forward-scattered light
Back-scattered light
Polarization state
Derived Parameters Particle diameter
Particle number concentration
Liquid water content (LWC)
Effective diameter (ED)
Median volume diameter (MVD)
Polarization ratios
Particle Size Range 0.65 - 30 µm
Number Conc. Range 20,000 particles per second
Typical Sample Area 0.17 mm2
Number of Size Bins 20, non-linearly spaced
Air Speed Range 10 - 250 m/sec
Sampling Frequency for Histogram Data Selectable, 0.04 to 20 seconds
Refractive Index Calibrated for 1.33 (the industry standard for water)
Light Collection Angles Forward Scatter: 13° - 47°
Back Scatter: 133° - 167°
Laser 658 nm, 50 mW
Data System Interface RS-422 serial interface
Calibration Glass beads and Polystyrene Latex Spheres
Routine Maintenance Window cleaning and glass bead calibration check
Recommended Service Annual cleaning and calibration at DMT service facility
Software Optional Particle Analysis and Display System (PADS) software
Power Requirements System Power: 115 VAC at 100W
Anti-ice Power: 115 VAC at 450W
Environmental Operating Conditions Temperature: -40 to 40 °C
Relative Humidity: 0 - 100%, non-condensing
Altitude: 0 - 50,000 feet (0 - 15,000 meters)
Weight ~10 kg
Probe Dimensions 39” L x 7” Diameter

Specifications are preliminary and subject to change without notice. The CPSPD is a Class 3B Laser Product.


Included Items

  • Instrument
  • Shipping case
  • Operator manual
  • One-year warranty
  • One day of training at DMT facility
  • Email and phone technical support

Accessories (Purchased separately)

  • PADS software and laptop


How to Order

Contact DMT for pricing or more information.


Phone: +001 303 440 5576
Fax: +001 303 440 1965

Selected Bibliography

D. Baumgardner, R. Newton, M. Kraemer, J. Meyer, A. Beyer, M. Wendisch, and P. Vochezer. "The Cloud Particle Spectrometer with Polarization Detection (CPSPD): A next generation open-path cloud probe for distinguishing liquid cloud droplets from ice crystals." Atmospheric Research Volume 142, 1 June 2014, pp. 2-14. Link