Cloud Combination Probe

The CCP is a multipurpose particle spectrometer that includes three Droplet instruments (CDP, CIP, and LWC) – plus temperature and relative humidity sensors – in a single package. Researchers use the CCP to obtain aerosol particle and cloud hydrometeor size distributions.


Get five measurements packaged into a single canister to enable optimized measurement of cloud particles prior to and during transition to precipitation.

See data on aerosol particle and cloud hydrometeor size distributions from 2 μm to 50 μm, two dimensional images and precipitation size distributions from 25 μm to 1550 μm (or 2 μm to 930 μm if the CIP component is ordered with 15-μm resolution), and liquid water content from 0.05 g/m3 to 3 g/m3.

Get more precise information on individual particle sizes with the optional PBP feature – including particle size in digital counts, individual particle time with μsec resolution, and inter-arrival particle time (IPT).

Use the optional grayscale imaging and fine-resolution features (for the CIP) to get more clarity on particle composition.

Reduce the incidence of particle artifacts with optional Korolev anti-shatter tips (CIP feature), and keep your CIP instrument performing optimally with optional 8 VDC or 115 VAC anti-ice heaters.

Particle imaging and particle light-scattering

The three Droplet instruments included in the CCP are the Cloud Imaging Probe (CIP), the Cloud Droplet Probe (CDP), 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 CDP is a forward-scattering optical spectrometer that accepts and sizes only particles that pass through a region of the laser beam with uniform power.
  • Forward-scattered light is collected, directed through a 50/50 optical beam splitter, then measured by photodetectors to determine size and depth of field.


  • 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.
Parameter SpecificationCDP SpecificationLWC Specification

Optical Array Probe with 64 elements: 62 sizing elements, end diodes reject

Light-scattering probe with 30 size binsTemperature-Controlled Hotwire Sensor
Measured Particle Size Range

12.5 µm – 1.55 mm (standard)

2 µm to 50 µmN/A; measured LWC range is 0 - 3 g/m3
Sample Area

Variable; depends on tip configuration and particle size

0.24 mm2N/A
Upper Concentration Range

Depends on particle size, but up to 500 particles/ cm3 for a CIP with standard tips and arm width

2,000 particles/cm33 g/m3
Air Speed Range

10 – 300 m/s for 25 μm resolution CIP; 10 – 180 m/s for 15 μm CIP

10 - 250 m/s10 - 200 m/s
Number of Size Bins


Sampling Frequency

1D histogram data: 0.05 to 25 Hz
2D image data: variable interval, when buffer fills

Selectable, 0.05 to 25 HzN/A

658 nm, 30 mW

658 nm, ~50 mWN/A
Non-absorbing Refractive Index


1.33 (the industry standard for water)N/A
Light Collection Angles


4° - 12°N/A
Auxiliary Parameters

Ambient Temperature
Relative Humidity
Static Pressure
Dynamic Pressure

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


29 lbs./13.2kg for probe and canister

Power Requirements

System Power bus: 28 VDC, 3A
Auxiliary bus (formerly “LWC bus”): 28 VDC, up to 8A (depends on LWC content)
CIP Anti-Ice bus: 28 VDC, 13A
CDP Anti-Ice bus:28 VDC, 7A

Environmental Operating Conditions

Temperature: -40 °C to +40°C (-40 °F to +104 °F)
RH: 0 – 100%, non-condensing
Altitude: 0 – 50,000 ft

  • PADS software and laptop
  • Data Acquisition System

Droplet offers a three-year service plan to ensure that your CCP continues to deliver high-quality data. This plan locks costs upfront at the time of funding application and covers annual calibration, alignment, cleaning, wear-item replacement, calibration documentation, and shipping. Specific services provided for the CCP include:

  • Shipping to and from Droplet facility for service
  • Incoming instrument evaluation and health check
  • Optics cleaning and alignment
  • Temperature sensor calibration
  • O-ring replacement
  • Hardware and connector replacement
  • Heater testing
  • Laser evaluation, adjustments, and alignment
  • Pitot calibration
  • Canister test
  • Cleaning and replacement of heater heatsink compound
  • Dump spot monitor check
  • Laser splitter block alignment
  • Offset voltage verification
  • Baseline amplitude verification
  • Baseline voltage evaluation on DSP board and PADS
  • Heater resistance evaluation
  • Reseal windows
  • Software, firmware, and antivirus update
  • Extreme cold testing of probe
  • Light test performed
  • Calibration of instrument using spinning disk calibrator
  • Wind tunnel test
  • Beam-mapping of instrument
  • 100% unit functionality test
  • Calibration Data, Wind Tunnel Report, Calibration Report, and Certificate of Calibration provided

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