Global Hawk - AFRC

The UHSAS is an optical-scattering, laser-based aerosol particle spectrometer for sizing particles in the 0.06 – 1 μm range. The instrument counts particles in up to 100 user-specified sizing bins, with a resolution as fine as 1 nm/bin. This high sensitivity makes the UHSAS ideal for aerosol research and filter testing.

A laser illuminates particles, which scatter light that is then collected by two pairs of Mangin optics. One pair of optics images onto a highly sensitive avalanche photodiode (APD) for detecting the smallest particles. The other pair images onto a low-gain PIN photodiode for detecting particles in the larger size range of the instrument. Each detector is amplified in a current-to-voltage stage that feeds into the analog electronics system. The amplification allows the system to detect particles as small as 60 nm.

The Unmanned Aircraft Systems (UAS) Chromatograph for Atmospheric Trace Species (UCATS) was designed and built for autonomous operation on remotely piloted aircraft, but has also been used on manned aircraft. It uses chromatography to separate atmospheric trace gases along narrow heated columns, followed by precise and accurate detection with electron capture detectors. There are currently three chromatography channels on UCATS, which measure nitrous oxide (N2O) and sulfur hexafluoride (SF6); CFC-11, CFC-12, CFC-113, and halon 1211; and chloroform (CHCl3) and carbon tetrachloride. On an earlier version of UCATS, with only two channels, we also measured methane, hydrogen, and carbon monoxide, along with N2O and SF6. In addition, there is a small ozone instrument and a tunable diode laser instrument for water vapor. Gas is pumped into the instruments from an inlet outside the aircraft, measured, and vented. UCATS has flown on the Altair UAS, the GV during HIPPO, the NASA Global Hawk UAS during the Global Hawk Pacific (GloPac) and ATTREX missions, where a record was set for the longest duration research flight (more than 28 hours), the DC-8 for ATom, and the ER-2 for DCOTSS. UCATS is relatively lightweight and compact, making it ideal for smaller platforms, but it is easily adaptable to a mid-size platform like the GV or Global Hawk. The data are used to measure sources and sinks of trace gases involved in climate and air quality, as well as transport through the atmosphere.

UCATS is three different instruments in one enclosure:

1. 3-channel (formerly 2-channel, up until 2020) gas chromatograph (GC)
2. Dual-beam ozone photometer (OZ)
3. Tunable diode laser (TDL) spectrometer for water vapor (WV)

Ozone (O₃) in the lower stratosphere (LS) is responsible for absorbing much of the biologically damaging ultraviolet (UV) radiation from the sunlight, and thus plays a critical role in protecting Earth's environment. By absorbing UV light, O₃ heats the surrounding air, leading to the vertical stratification and dynamic stability that define the stratosphere. Halogen species from anthropogenic compounds such as CFCs can cause significant damage to the O₃ layer in the LS and have led to the formation of the Antarctic ozone hole. Accurate measurement of O₃ in the LS is the first step toward understanding and protecting stratospheric O₃. The UAS Ozone Photometer was designed specifically for autonomous, precise, and accurate O₃ measurements in the upper troposphere and lower stratosphere (UT/LS) onboard the NASA Global Hawk Unmanned Aircraft System (GH UAS) and other high altitude research platforms such as the ER-2 and WB-57. With a data rate of 2 Hz, the instrument can provide high-time-resolution, detailed information for studies of O₃ photochemistry, radiation balance, stratosphere-troposphere exchange, and air parcel mixing in the UT/LS. Furthermore, its accurate data are useful for satellite retrieval validation.  Contacts: Troy Thornberry, Ru-Shan Gao

Ozone (O3) in the lower stratosphere (LS) is responsible for absorbing much of the biologically damaging ultraviolet (UV) radiation from the sunlight, and thus plays a critical role in protecting Earth's environment. By absorbing UV light, O3 heats the surrounding air, leading to the vertical stratification and dynamic stability that define the stratosphere. Manmade halogen compounds, such as CFCs, cause significant damage to the O3 layer in the LS and lead to the formation of the Antarctic ozone hole. Accurate measurement of O3 in the LS is the first step toward understanding and protecting stratospheric O3. The Ozone Photometer was designed specifically for autonomous, precise, and accurate O3 measurements in the upper troposphere and lower stratosphere (UT/LS). Flown for thousands of hours onboard the NASA ER-2, NASA WB-57, and NSF GV high-altitude aircraft, this instrument has played a key role in improving our understanding of O3 photochemistry in the UT/LS. Furthermore, its accurate data has been used, and continues to be highly sought after, for satellite validation, and studies of radiation balance, stratosphere-troposphere exchange, and air parcel mixing. Contacts: Ru-Shan Gao, David Fahey, Troy Thornberry, Laurel Watts, Steve Ciciora

The Cloud Droplet Probe (CDP), manufactured by Droplet Measurement Technologies, measures the concentration and size distribution of cloud droplets in the size range from 2-50 µm. The instrument counts and sizes individual droplets by detecting pulses of light scattered from a laser beam in the near-forward direction, using a sample area of 0.24 mm2 or a sample rate of 48 cm3 at a flight speed of 200 m/s. The probe is mounted in an underwing canister and is designed to operate at up to 200 m/s; the G-V often exceeds this flight speed, but usually not in penetrations of clouds containing cloud droplets. Droplet sizes are accumulated in 30 bins with variable sizes, as specied in the header of the netCDF data files. Measurements are usually provided at a rate of 1 Hz in the standard data files but can be made available at 10 Hz in special high-rate processing. The instrument is similar to, and might be considered a high-speed replacement for, the Forward Scattering Spectrometer Probe. At high droplet concentration (> 500 cm-3), coincidence losses have been observed with this probe, and these are especially serious at G-V flight speeds. The probe is designed for cloud droplets, and its response to ice crystals is not intended to be quantitative; measurements in ice clouds should not be used except as qualitative indications of cloud.

ULH measures water vapor at high accuracy in the upper troposphere and lower stratosphere to meet the following science objectives:

1. validation and scientific collaboration with NASA earth-monitoring satellite missions, principally the Aura satellite, http://aura.gsfc.nasa.gov/

2. observations of stratospheric trace gases in the upper troposphere and lower stratosphere from the mid-latitudes into the tropics,

3. sampling of polar stratospheric air and the break-up fragments of the air that move into the mid-latitudes, The ULH flights on Global Hawk will advance the state of the art technologically with remote command and control. ULH will provide real-time in-situ stratospheric water vapor measurements from Global Hawk. Additionally, ULH will make continuous measurements during long-duration flights up to 33 hours, which would be impossible with manned aircraft.

The advantages of ULH over other hygrometers are:

• Small and lightweight instrument package,
• No outgassing (achieved by mounting the open-path optical cell in the free air stream),
• Fast time response measurements in and out of clouds, without contamination,
• Accurate with a low detection limit <1 ppmv.

The TWiLiTE instrument is a compact, rugged direct detection scanning Doppler lidar designed to measure wind profiles in clear air from 18 km to the surface. TWiLiTE operates autonomously on NASA research aircraft (ER-2, DC-8, WB-57, Global Hawk). Initial engineering flight tests on the NASA ER-2 in 2009 demonstrated autonomous operation of all major systems. TWiLiTE will be reconfigured to fly on the NASA Global Hawk as part of the Hurricane and Severe Storm Sentinel Venture Class Mission.

In early 2000, the Ames Atmospheric Radiation Group completed the design and development of an all new Solar Spectral Flux Radiometer (SSFR). The SSFR is used to measure solar spectral irradiance at moderate resolution to determine the radiative effect of clouds, aerosols, and gases on climate, and also to infer the physical properties of aerosols and clouds. Additionally, the SSFR was used to acquire water vapor spectra using the Ames 25-meter base-path multiple-reflection absorption cell in a laboratory experiment. The Solar Spectral Flux Radiometer is a moderate resolution flux (irradiance) spectrometer with 8-12 nm spectral resolution, simultaneous zenith and nadir viewing. It has a radiometric accuracy of 3% and a precision of 0.5%. The instrument is calibrated before and after every experiment, using a NIST-traceable lamp. During field experiments, the stability of the calibration is monitored before and after each flight using portable field calibrators. Each SSFR consists of 2 light collectors, which are either fix-mounted to the aircraft fuselage, or on a stabilizing platform which counteracts the movements of the aircraft. Through fiber optic cables, the light collectors are connected to 2 identical pairs of spectrometers, which cover the wavelength range from (a) 350 nm-1000 nm (Zeiss grating spectrometer with Silicon linear diode array) and (b) 950 nm - 2150 nm (Zeiss grating spectrometer with InGaAs linear diode array). Each spectrometer pair covers about 95% of the incoming solar incident irradiance spectrum.