Dr Nicholas Marsden

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Instrument Support Level 4

Instrument Support Level

Instrument Support Level 4

Manufacturer & Model

Spec. Inc, USA. CPI

CEDA Archive Name


Data Products

aerosol-size-distribution, image

Insurance Value


Physical Dimensions

See page for details


See page for details

Daily Facility Charge



Cloud Particle Imager

The CPI can image and count particles in the size range of 15-2500um, with the images having a nominal 2.3um resolution. Image analysis and data processing software provided with the probe takes particle size information (including area and volume) and ice crystal habit classification from the images to produce histograms etc.

The CPI is especially suitable for use in ice and mixed-phase clouds which typically have relatively low (compared to water clouds) particle concentration of 1000/L.

The CPI may be used in much higher particle concentrations, but under these conditions, while particle spectra are reliable, absolute particle concentrations are not due to coincidence errors in the particle detection system.

While designed for aircraft use, and able to operate at any aircraft speed and altitude, the CPI, with the use of a suitable aspiration device may also be used for ground-based or lab studies.

The unit available here is a 3V-CPI (3-View Cloud Particle Imager). This is essentially a 400 frame per second CPI probe integrated with a 2D-S probe.

The SPEC-3V-CPI (3V-CPI; 3 View Cloud Particle Imager) is a probe for measuring the size, shape, and concentration of airborne particles. It has two independent shadow sensor channels to increase counting efficiency and to produce stereoscopic images. Each of these channels consists of a laser beam approximately 1.6 mm in width and 61 mm in open path length. The beams are aimed at 128 element photo-detector arrays (one per channel). As particles pass through the sample volume, a series of one-dimensional slices of an image is built up, as elements of the photo-detector arrays are shadowed from the laser illumination. These slices are built up into two-dimensional shadow images of particles at a rate determined by the aircraft airspeed. When particles are detected by the 2D shadow sensors, a pulsed imaging laser (810 nm; 100 W; 200 ns min, 0.04% duty cycle; 1.0 kHz max repetition) is triggered to illuminate the particles for imaging using a magnified CCD camera (2.21 μm per pixel).

Due to the beam and photodetector geometry, the probe is sensitive to particles between 10 μm and 2263 μm, – 2D detector element size up to CCD array size. It’s very high sample volume and extremely fast sample rate means that a large number of particles are sampled, giving high spatial resolution at aircraft operating speeds.

Sizing accuracy is checked for consistency against other cloud probes such as 2DS and CIP. Periodic calibrations take place in the laboratory in Manchester, but there is no requirement for field calibration. The sizing performance of the probe is very stable.

There are no servicing requirements apart from the cleaning of the optical windows at regular intervals.

  • Normally only cotton swabs and deionised water are required. These will be supplied by the IS operating the probe.
  • Instrument Insurance
    • This system must be insured by the user for £100K and covers loss, theft or damage to the instrument: damage is that over and above general wear and tear. The system has been designed to be rugged and autonomous. Even so, the end-user must respect the fact that the system is a precision optical instrument that must be treated with great care.
    • The user is responsible for the instrument from the time it leaves the AMOF to the time it is returned and signed off as in an acceptable operating condition by the IS: this will be done as soon as is possible on its return.
  • Public Liability Insurance
    • The AMOF is not liable for any damage or injury arising from the deployment or operation of this instrument when unattended by the IS.
  • Shipping Expenses
    • The user is liable for all costs arising from the shipping of the instrument both to and from a deployment.
  • IS T&S
    • The user is responsible for coving the travel and subsistence expenses of the IS while attending the instrument.

The system when packed ready for shipping consists of two boxes:

One flight case with wheels containing the probe, measuring 67 x 87 x 37 cm and weighing approximately 45 kg.

Typically one aluminium box containing the data acquisition system, monitor, keyboard, power transformer and spares. Size is 78 x 58 x 41 cm. This normally weighs around 40 kg.

For use on the FAAM aircraft, 3v-CPI must be used in conjunction with the Manchester cloud physics rack. Please contact the IS for further information.

The design of ground-based cloud experiments is beyond the scope of this document. Please contact the IS for further information or to discuss your requirements.


Eye safety
  • The CPI is a class 1 laser device when the covers are in place. Cleaning of the optical windows should not take place with the lasers powered on. With the covers off, it becomes a lass 3R device. Only the IS is permitted to conduct maintenance work with the covers removed. Risk assessments and local rules for usage are available from the IS on request.
Manual handling
  • The probe mass is approximately 20 kg. It can be only safely handled by a single person under certain very limited circumstances. The packed mass of 50 kg means the supplied wheels must be used to transport the shipping case.
Electrical safety
  • Under normal circumstances, no live electrical connections are exposed. High voltages exist inside the probe and data acquisition system, so the covers must never be removed except in the presence of the IS.
Attended operation
  • No intrinsic hazards during operation have been identified. Most hazards are a result of the operating environment.

Weight (not including shipping case): ~20 kg

Power: Shown in table

Operation temperature: 20°C to -60°C

Current Power
110 V @ 400 Hz* 9.5 A 1045 W
110 V @ 400 Hz* 9.5 A 1045 W
110 V @ 60 Hz** 1.5 A 165 W
Total 2255 W

Power consumption

* For aircraft use. Can be 50Hz.

** Includes data acquisition system.

The CPI and  3V-CPI both produce binary files containing compressed particle images, timestamps and housekeeping variables.

Field Data
  • 3V – CPI:
    • Data are split into two streams. Data from the greyscale CCD camera are output separately to those from the shadow probe “triggering” portion of the probe.
  • The user can download (but not delete) this data from the instrument but it should be noted that this data will not have been quality controlled.
Archive Data
  • Data is provided in NetCDF files following the AMF data standard
  • Files contain no more than 24hr of data.
  • Instrument name is
    • ncas-cpi-1
  • The data product(s) associated with this instrument:
    • aerosol-size-distribution,
    • image