Photo: the CAPS mounted on a Twin Otter research aircraft. Photo courtesy of British Antarctic Survey.
The CAPS combines multiple instruments in one flight canister, resulting in an exceptionally broad array of data:
Two optional software packages are available for CAPS users. The Particle Analysis and Display System (PADS) allows for instrument control and real-time data display.
The second software package, the Optical Array Shadow Imaging Software (OASIS), facilitates post-processing particle analysis. More information about these two packages is given below.
PADS displays a user-friendly virtual instrument panel that enables the user to do the following tasks:
OASIS, shown at right, is designed for rigorous post-processing analysis. It provides additional particle statistics beyond those generated by PADS. In addition, OASIS allows users to filter particles by various criteria, including particle area, particle shape, area fraction, and inter-arrival time. Written in IGOR Pro, OASIS leverages IGOR’s robust statistical analysis features for enhanced data analysis and graphing capability.
The three DMT instruments included in the CAPS are the Cloud Imaging Probe (CIP), the Cloud and Aerosol Spectrometer (CAS), and the Hotwire Liquid Water Content Sensor (Hotwire LWC).
The CIP, which measures larger particles, operates as follows. Shadow images of particles passing through a collimated laser beam are projected onto a linear array of 64 photodetectors. The presence of a particle is registered by a change in the light level on each diode. The registered changes in the photodetectors are stored at a rate consistent with probe velocity and the instrument’s size resolution. 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. A slice must be stored each time interval that the particle advances through the beam a distance equal to the resolution of the probe.
The CAS, which measures smaller particles, relies on light-scattering rather than imaging techniques. Particles scatter light from an incident laser, and collecting optics guide the light scattered in the 4° to 12° range into a forward-sizing photodetector. This light is measured and used to infer particle size. Backscatter optics also measure light in the 168° to 176° range, which allows determination of the real component of a particle’s refractive index for spherical particles.
The Hotwire LWC instrument estimates liquid water content using a heated sensing coil. The system maintains the coil at a constant temperature, usually 125 °C, and measures the power necessary to maintain this temperature. More power is needed to maintain the temperature as droplets evaporate on the coil surface and cool the surface and surrounding air. Hence, this power reading can be used to estimate LWC. Both the LWC design and the optional PADS software contain features to ensure the LWC reading is not affected by conductive heat loss.
|Parameter||CIP Specification||CAS Specification||LWC Specification|
|Technique||Optical Array Probe with 64 elements: 62 sizing elements, end diodes reject||Forward and Back Scatter Light Sensors||Temperature-Controlled Hotwire Sensor|
|Measured Particle Size Range||12.5 µm – 1.55 mm (standard)||0.51 µm to 50 µm||N/A; measured LWC range is 0 - 3 g/m3|
|Sample Area||10 cm x 1.55 mm||11.1 mm x 120 µm||N/A|
|Upper Concentration Range||Depends on particle size, but up to 500 particles/ cm3 for a CIP with standard tips and arm width||Greater than 1,000 particles/cm3 after corrections for coincidence that are about 25% at 800 and 30% at 1,000 particles/cm3||3 g/m3|
|Air Speed Range||10 - 300 m/s||10 - 200 m/s||10 - 200 m/s|
|Number of Size Bins||62||Selectable; 10, 20, 30, or 40||N/A|
|Sampling Frequency||1D histogram data: 0.05 to 40 Hz
2D image data: variable interval, when buffer fills
|Selectable, 0.05 to 40 Hz||N/A|
|Laser||658 nm, 30 mW||658 nm, ~50 mW||N/A|
|Calibration Verification||Spinning glass disk with opaque dots of known size||Precision glass beads and latex spheres for sub-micron range||Not Required|
|Light-scattering Parameters||N/A||Non-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/A||N/A|
|Data System Interface:||2D CIP data: RS-422, High Speed, 4 Mb/sec Baud Rate
System data: RS-232 or RS-422, 56.6 kb/sec Baud Rate
|Optional Software||Particle Analysis and Display System (PADS) for all instruments
Optical Array Shadow Imaging System (OASIS) for CIP
|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
|Routine Maintenance||DMT recommends conducting basic instrument performance checks and inspecting the CIP optical windows before a flight. A weekly calibration check of the CAS and CIP is also recommended.|
Specifications are subject to change without notice. CAS specifications apply to both standard CAS and CAS with polarization.
Contact DMT for pricing or more information.
Phone: +001 303 440 5576
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