NASA - National Aeronautics and Space Administration

The MODIS Airborne Simulator (MAS) is a multispectral scanner configured to approximate the Moderate-Resolution Imaging Spectrometer (MODIS), an instrument to be orbited on the NASA EOS-AM1 platform. MODIS is designed to measure terrestrial and atmospheric processes. The MAS was a joint project of Daedalus Enterprises, Berkeley Camera Engineering, and Ames Research Center. The MODIS Airborne Simulator records fifty spectral bands.

The Harvard Water Vapor (HWV) instrument combines two independent measurement methods for the simultaneous in situ detection of ambient water vapor mixing ratios in a single duct. This dual axis instrument combines the heritage of the Harvard Lyman-α photo-fragment fluorescence instrument (LyA) with the newly designed tunable diode laser direct absorption instrument (HHH). The Lyman-α detection axis functions as a benchmark measurement, and provides a requisite link to the long measurement history of Harvard Lyman-α aboard NASA’s WB-57 and ER-2 aircraft [Weinstock et al., 1994; Hintsa et al., 1999; Weinstock et al., 2009]. The inclusion of HHH provides a second high precision measurement that is more robust than LyA to changes in its measurement sensitivity [Smith et al., in preparation]. The simultaneous utilization of radically different measurement techniques facilitates the identification, diagnosis, and constraint of systematic errors both in the laboratory and in flight. As such, it constitutes a significant step toward resolving the controversy surrounding water vapor measurements in the upper troposphere and lower stratosphere.

The MASTER is similar to the MAS, with the thermal bands modified to more closely match the NASA EOS ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite instrument, which was launched in 1998. It is intended primarily to study geologic and other Earth surface properties. Flying on both high and low altitude aircraft, the MASTER has been operational since early 1998.

Instrument Type: Multispectral Imager
Measurements: VNIR/SWIR/MWIR/LWIR Imagery

The High Altitude Monolithic Microwave integrated Circuit (MMIC) Sounding Radiometer (HAMSR) is a microwave atmospheric sounder developed by JPL under the NASA Instrument Incubator Program. Operating with 25 spectral channels in 3 bands (50-60 Ghz, 118 Ghz, 183 Ghz), it provides measurements that can be used to infer the 3-D distribution of temperature, water vapor, and cloud liquid water in the atmosphere, even in the presence of clouds. The new UAV-HAMSR with 183GHz LNA receiver reduces noise to less than a 0.1K level improving observations of small-scale water vapor. HAMSR is mounted in payload zone 3 near the nose of the Global Hawk.

HAMSR was designed and built at the Jet Propulsion Laboratory under the NASA Instrument Incubator Program and uses advanced technology to achieve excellent performance in a small package. It was first deployed in the field in the 2001 Fourth Convection and Moisture Experiment (CAMEX-4) - a hurricane field campaign organized jointly by NASA and the Hurricane Research Division (HRD) of NOAA in Florida. HAMSR also participated in the Tropical Cloud Systems and Processes (TCSP) hurricane field campaign in Costa Rica in 2005. In both campaigns HAMSR flew as a payload on the NASA high-altitude ER-2 aircraft. It was also one of the payloads in the 2006 NASA African Monsoon Multidisciplinary Activities (NAMMA) field campaign in Cape Verde - this time using the NASA DC-8. HAMSR provides observations similar to those obtained with microwave sounders currently operating on NASA, NOAA and ESA spacecraft, and this offers an opportunity for valuable comparative analyses.

The MAMS is a modified Daedalus Scanner flown aboard the ER-2 aircraft. It is designed to study weather related phenomena including storm system structure, cloud-top temperatures, and upper atmospheric water vapor. The scanner retains the eight silicon-detector channels in the visible/near-infrared region found on the Daedalus Thematic Mapper Simulator, with the addition of four channels in the infrared relating to specific atmospheric features.

The scanner views a 37 kilometer wide scene of the Earth from the ER2 altitude of about 20 kilometers. Each MAMS footprint (individual field of view) has a horizontal resolution of 100 meters at nadir. Since the ER2 travels at about 208 meters per second, a swath of MAMS data 37 by 740 kilometers is collected every hour. The nominal duration of an ER2 flight is 6 hours (maximum of about 7 hours).

The Harvard CRDS/ICOS instrument is an absorption spectrometer that uses the relatively new and highly sensitive techniques of integrated cavity output spectroscopy (ICOS) and cavity ringdown spectroscopy (CRDS) with a high-finesse optical cavity and a cw quantum cascade laser (QCL) source. The primary spectroscopic technique employed is ICOS, in which intra-cavity absorption is measured from the steady-state output of the cavity. Light from a high power, tunable, single mode, solid-state laser source is coupled into a cavity consisting of two concave, highly reflective mirrors (R ≈ 0.9999), through which air continuously flows. The laser is scanned over a spectral region of 1–2 cm-1 containing an absorption feature, and the cavity output is detected by an LN2-cooled HgCdTe detector. The resultant output approximates an absorption spectrum with an effective pathlength of > 5 km, far greater than that of standard multipass Herriott or White cells.

The design of the newly developed total water instrument is based on the same principles as the water vapor instrument, and is intended to fly in conjunction with it. Conceptually, the total water instrument can be thought of as containing four subsystems:
1. An inlet through which liquid and/or solid water particles can be brought into an instrument duct without perturbing the ambient particle density.
2. A heater that efficiently evaporates the liquid/solid water before it reaches the detection axis.
3. Ducting through which the air flows to the detection axis without perturbing the (total) water vapor mixing ratio.
4. A water vapor detection axis that accurately and precisely measures the total water content of the ambient air.

The Multiple-Angle Aerosol Spectrometer Probe (MASP) determines the size and concentration of particles from about 0.3 to 20 microns in diameter and the index of refraction for selected sizes. Size is determined by measuring the light intensity scattered by individual particles as they transit a laser beam of 0.780µm wavelength. Light scattered from particles into a cone from 30 to 60 degrees forward and 120 to 150 degrees backwards is reflected by a mangin mirror through a condensing lens to the detectors. A comparison of the signals from the open aperture detector and the masked aperture detector is used to accept only those particles passing through the center of the laser beam. The size of the particle is determined from the total scattered light. The index of refraction of particles can be estimated from the ratio of the forward to back scatter signals. A calibration diode laser is pulsed periodically during flight to ensure proper operation of the electronics. The shrouded inlet minimizes angle of attack effects and maintains isokinetic flow through the sensing volume so that volatilization of particles is eliminated.

The Multiple Aerosol Collection System contains an impactor collector which permits the collection of particles on electron microscope grids for later chemical-constituent analysis. The collector consists of a two stages. In the first stage the pressure of the sample is reduced by a factor of two without loosing particles by impaction on walls. The second stage consists of a thin plate impactor which collects efficiently even at small Reynolds numbers. The system collects particles as small as 0.02 micron at WB-57 cruise altitudes. As many as 24 samples can be collected in a flight.

OH is detected by direct laser induced fluorescence in the (0-1) band of the 2?-2? electronic transition. A pulsed dye-laser system produces frequency tunable laser light at 282 nm. An on-board frequency reference cell is used by a computer to lock the laser to the appropriate wavelength. Measurement of the signal is then made by tuning the laser on and off resonance with the OH transition.

Stratospheric air is channeled into the instrument using a double-ducted system that both maintains laminar flow through the detection region and slows the flow from free stream velocity (200 m/s) to 40 m/s. The laser light is beam-split and directed to two detection axes where it passes through the stratospheric air in multipass White cells.

Fluorescence from OH (centered at 309 nm) is detected orthogonal to both the flow and the laser propagation using a filtered PMT assembly. Optical stability is checked periodically by exchanging the 309 nm interference filter with a filter centered at 302 nm, where Raman scattering of N2 is observed.

HO2 is measured as OH after chemical titration with nitric oxide: HO2 + NO → OH + NO2. Variation of added NO density and flow velocity as well as the use of two detection axes aid in diagnosis of the kinetics of this titration. Measurements of ozone (by uv absorption) and water vapor (by photofragment fluorescence) are made as diagnostics of potential photochemical interference from the mechanism: O3 + hv (282 nm) → O(1D) + O2, followed by: O(1D) + H2O → OH + OH