Cloud, Aerosol, and Precipitation Spectrometer with Depolarization

The CAPS-DPOL is a multipurpose, research-grade cloud spectrometer that includes three Droplet instruments (CIP, LWC, and CAS); temperature and relative humidity sensors; and polarization measurement to discriminate between water and ice.


Combine multiple probes with ranges optimized to measure cloud particles prior to and during transition to precipitation.

CAS measures aerosol particle and cloud hydrometeor size distributions from 2 µm to 50 µm; CIP measures precipitation size distributions from 25 µm to 1550 µm, and LWC measures liquid water content from 0.01 g/m3 to 3 g/m3, along with aircraft velocity, and atmospheric temperature and pressure.

Gather data on particle optical properties (refractive index), as well as particle shape assessments (discrimination between water and ice for probes with depolarization feature).

Particle imaging, polarization detection, and hotwire sensing

The three Droplet instruments included in the CAPS-DPOL are the Cloud Imaging Probe (CIP), the Cloud and Aerosol Spectrometer with Depolarization (CAS-DPOL), and the Hotwire Liquid Water Content Sensor (Hotwire LWC).


  • Shadow images of particles passing through a collimated laser beam are projected onto a linear array of 64 photodetectors to determine presence of particles.
  • Particle images are reconstructed from individual “slices,” where a slice is the state of the 64-element linear array at a given moment in time.


  • The CAS-DPOL collects forward-scattered light to determine particle size, and polarized back-scatter light to differentiate between spherical and aspherical particles.


  • The LWC features a coiled wire that is maintained at 150 °C, which acts as variable resistance in a Wheatstone Bridge circuit.
  • The resistance of the sensing coil is directly proportional to its temperature.
  • Power dissipated by the sensor to maintain temperature is used to calculate vaporization, and in turn, liquid water content.
ParameterCIP SpecificationCAS SpecificationLWC Specification
Technique Optical Array Probe with 64 elements: 62 sizing elements, end diodes rejectForward- and Back-Scatter Light SensorsTemperature-Controlled Hotwire Sensor
Measured Particle Size Range 12.5 µm – 1.55 mm (standard)0.51 µm to 50 µmN/A; measured LWC range is 0 - 3 g/m3
Sample Area 10 cm x 1.55 mm11.1 mm x 120 µmN/A
Upper Concentration Range Depends on particle size, but up to 500 particles/ cm3 for a CIP with standard tips and arm widthGreater than 1,000 particles/cm3 after corrections for coincidence that are about 25% at 800 and 30% at 1,000 particles/cm33 g/m3
Air Speed Range 10 - 300 m/s10 - 200 m/s10 - 200 m/s
Number of Size Bins 62Selectable; 10, 20, 30, or 40N/A
Sampling Frequency 1D histogram data: 0.05 to 40 Hz 2D image data: variable interval, when buffer fillsSelectable, 0.05 to 40 HzN/A
Laser 658 nm, 30 mW658 nm, ~50 mWN/A
Light-scattering Parameters N/ANon-absorbing refractive index: 1.3 – 1.7
Light collection angles: 4° - 12°, 168° - 176°
Auxiliary Parameters Ambient Temperature, Relative Humidity, Static Pressure, Dynamic Pressure (CIP)N/AN/A
Data System Interface: 2D CIP data: RS-422, High Speed, 4 Mb/sec Baud Rate System data: RS-422, 56.6 kb/sec Baud Rate
Weight 45 lbs./20.4 kg
Power Requirements 28VDC: 10A for probe system, and 45A for anti-ice heaters, optional AC voltages for anti-ice heaters
Environmental Operating Conditions Temperature: 0 – 40°C (32 – 104 °F) RH: 0 – 100%, non-condensing
  • PADS software and laptop
  • Data Acquisition System

The Lifecycle Care Program ensures CAPS-DPOL 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.