4STAR in ORACLES onboard NASA P3

Sam at P3 arrival in Sao Tome

Sam at P3 arrival in Sao Tome - ORACLES

Flying over cloud deck during PRF02Y17

Glory, cloudbow and Brocken spectre from Nadir camera (PRF01Y17)


Hawkeye is a combination cloud particle probe. The instrument includes four probes in one.

Probe 1: The Fast Cloud Droplet Probe (FCDP) records individual particle statistics and digitizes waveform.

Probes 2-3: 2D-S 10-µm channel and 50-µm channel also trigger CPI.

Probe 4: 400 frame per second Cloud Particle Imager (CPI).

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Advanced Vertical Atmospheric Profiling System

The Advanced Vertical Atmospheric Profiling System (AVAPS) is the dropsonde system for the Global Hawk. The Global Hawk dropsonde is a miniaturized version of standard RD-93 dropsondes based largely on recent MIST driftsondes deployed from balloons. The dropsonde provides vertical profiles of pressure, temperature, humidity, and winds. Data from these sondes are transmitted in near real-time via Iridium or Ku-band satellite to the ground-station, where additional processing will be performed for transmission of the data via the Global Telecommunications System (GTS) for research and operational use. The dispenser is located in zone 61 in the Global Hawk tail and is capable of releasing up to 88 sondes in a single flight.

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Rosemount Icing Detector

The RICE is a magnetostrictive oscillation probe with a sensing cylinder 6.35 mm in diameter and 2.54 cm in length. Ice buildup on the sensing cylinder causes the frequency of oscillation to change, which can be related to the rate of ice accretion and hence the cloud liquid water content (LWC). When approximately 0.5 mm of ice has accumulated, a heater melts the ice, which is shed into the air stream. The heater cycle is approximately 5 s, and the cylinder normally requires an additional 5–10 s to cool down to a temperature where it can begin accreting ice again.

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Cloud Aerosol and Precipitation Spectrometer

Measures concentration and records images of cloud particles from approximately 50-1600 microns in diameter with a resolution of 25 microns per pixel. Measures cloud droplet and aerosol concentrations within the size range of 0.5-50 microns.

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. Optional grayscale imaging gives three levels of shadow recording on each photodetector, allowing more detailed information on the particles.

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.

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