AIRBORNE MICROPHYSICS AND AEROSOL INSTRUMENTS

(A. Heymsfield)

Video Ice Particle Sampler (VIPS): The VIPS is an electro-optical instrument used to collect and record a continuous sample of cloud particles down to 5 microns. The resulting imagery is available for realtime, in-flight evaluation of cloud conditions and for post-flight habit classification and size distribution analysis. of secondary importance to objectives 1 and 2, important for objective 3. The instrument is calibrated with test beads and is accurate to a few microns resolution. It has performed in a number of experiments, including CEPEX.

Multiangle Aerosol Spectrometer Probe (MASP): The MASP determines the size and concentration of particles 0.3 to 20 microns in diameter and the refractive index for particles 0.4 to 0.7 microns in diameter. The light scattered from individual particles passing through a 0.780 micron wavelength laser beam is collected over angles of 30 to 60 degrees in the forward direction and 120 to 150 degrees in the backward direction. The index of refraction is determined by comparing the ratio of forward to backscattered light to the total scattered light and finding the best fit to Mie scattering theory. The size of the particle is determined from the total scattered light once the refractive index is known. of critical importance for objective 1, indirect effects. It is calibrated with test beads in the laboratory. It's performance characteristics have not been well established. It has performed on several NASA missions over the Antarctic, Arctic, and mid-latitude locations.

1DC: A one-dimensional cloud probe is an instrument that measures the sizes of particles in one dimension by measuring the shadowing on a one-dimensional grid of photodetectors as a particle passes through a laser beam. Particles between about 50 to 1000 microns can be detected by this instrument.

This is a vital instrument for stated objective 1, indirect effects, and lesser so for objectives 2 and 3. This is an off-the-shelf Particle Measuring Systems instrument. It's performance has recently been documented in the Florida area cumulus project (SCMI). It is calibrated with glass beads and projectiles. It has a good track record in the field, although it's performance is now first being quantified.

2DC: A two-dimensional cloud probe is an instrument that measures the sizes of particles in two dimensions. A one-dimensional grid of photodetectors measures the shadowing on a grid of photodetectors as a particle passes through a laser beam; the grid is attached to a high-speed front end operating system that enables several bits of shadow information to be encoded from the same particle, hence the transit scans give two-dimensional images. Particles between about 40 microns to greater than 1 mm can be detected by this instrument.

This probe is of vital importance for stated objective 1, indirect effects. The instrument is an off-the-shelf Particle Measuring Systems probe, and is calibrated with test beads, wires, and projectiles. It's performance for raindrops is well documented. This and many other 2DC probes have been the main means of measuring particle size spectra in clouds for over twenty years.

Forward Scattering Spectrometer Probe (FSSP): A forward-scattering spectrometer measures the amount of light that is forward scattered by a particle as it passes through a focused laser beam. The particle diameter is predicted by the amount of scattered light according to Mie theory for water droplets. Depending upon the model, a FSSP can measure particles between about 1 micron and 45 microns.

This is a vital instrument for stated objective 1, indirect effects, and lesser so for objectives 2 and 3. This is an off-the-shelf Particle Measuring Systems instrument. It is calibrated with glass beads and projectiles. It is robust, and it's performance characteristics in liquid water regions have now been thoroughly established.

Cryogenic Frost-Point Hygrometer: The instrument is a chilled-mirror, condensation- type hygrometer that uses optical detectors for condensate sensing. The use of a thermo- optical servo system coupled with a liquid nitrogen heat sink allows the instrument to respond rapidly and maintain a large dew-point depression even at low temperatures.

The instrument is of no importance for objective 1 or 2, and of great importance for objective 3. It has been thoroughly calibrated in an environmental chamber and used in the field for many years.

Rosemount Icing Detector: The sensing unit is a cylindrical assembly that vibrates axially at a resonant frequency of 40 kHz. Once ice begins to accumulate on the sensor, the added mass decreases the resonant frequency of the cylinder. This frequency is compared to a reference frequency, providing an output signal proportional to the accumulated mass.

This instrument is of no importance for objective 1 or 2, and of great importance for objective 3. It is an off-the-shelf instrument, is robust and has been calibrated empirically in the field.

Rosemount Temperature Probe: The probe is a standard Rosemount unit, de-iced version. Probe dynamic heating effects must be evaluated through aircraft "speed runs" to ensure accurate air temperature measurements.

This instrument is of great importance for objectives 1 and 3. It is an off-the-shelf instrument, and is calibrated in tower-fly by's and intercomparisons. It is accuracy to +/- 0.5 C. This or a similar probe is used on most commercial aircraft.

NCAR Dropsonde: This is a digital instrument which provides temperature, relative humidity, and GPS-derived winds each 5 m from the aircraft level (from which the instrument was dropped) to the ocean surface. The elements are from the Vaisala Met Package, and the GPS receiver is manufactured by Vaisala.

This instrument is of moderate to great importance for objectives 1 and 3. The instrument is relatively new, and has not been thoroughly tested. It is calibrated by Vaisala, and comparison with radiosondes and other instruments for accuracy.

mm cloud rada: this is a millimeter wavelenght Doppler radar developed by the University of Massachusetts and flown aboard the Universityu of Wyoming's King Air aircraft.

Getting use of this instrument for INDOEX may be problematical, but it is of significant importance in looking at locations of drizzle for objective 1, indirect effects. It's precise calibration is not of importance. The radar is robust, and has been used in a number of experiments by the University of Wyoming.

PVM-100A: This is an optical instrument that looks at the near-forward scattered light from particles passing through its 1.25 cm3 sensitive volume. The scattered light is weighed by spatial filtering as a function of scattering angle to achieve two outputs: one proportional to the second moment of the particle distribution and the other proportional to the third moment. Rigorous for spherical droplets, these outputs are approximately proportional to the projected area of irregular particles such as ice crystals. Given additional information as to crystal habit, ambient ice crystal water content, ice crystal sizes (~5 to 75 micron diameter range), ice crystal surface area, and effective radius may be estimated.

This instrument is of significant importance for Objective 1, indirect effects, and Objective 3. The instrument has been flown on a few missions by NASA, and has been calibrated in the Colorado State Universityıs Environmental Chamber. The instrument has also been flown on the NCAR C130, and tested against other instruments which measure similar parameters.