Synonyms: 
Water Vapor
Water

High Altitude Monolithic Microwave integrated Circuit (MMIC) Sounding Radiometer

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.

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Diode Laser Hygrometer

The DLH has been successfully flown during many previous field campaigns on several aircraft, most recently ACTIVATE (Falcon); FIREX-AQ, ATom, KORUS-AQ, and SEAC4RS (DC-8); POSIDON (WB-57); CARAFE (Sherpa); CAMP2Ex and DISCOVER-AQ (P-3); and ATTREX (Global Hawk). This sensor measures water vapor (H2O(v)) via absorption by one of three strong, isolated spectral lines near 1.4 μm and is comprised of a compact laser transceiver and a sheet of high grade retroflecting road sign material to form the optical path. Optical sampling geometry is aircraft-dependent, as each DLH instrument is custom-built to conform to aircraft geometric constraints. Using differential absorption detection techniques, H2O(v) is sensed along the external path negating any potential wall or inlet effects inherent in extractive sampling techniques. A laser power normalization scheme enables the sensor to accurately measure water vapor even when flying through clouds. An algorithm calculates H2O(v) concentration based on the differential absorption signal magnitude, ambient pressure, and temperature, and spectroscopic parameters found in the literature and/or measured in the laboratory. Preliminary water vapor mixing ratio and derived relative humidities are provided in real-time to investigators.

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Tropospheric Ozone and Tracers from Commercial Aircraft Platforms

Ozone is measured in a dual-beam ultraviolet (254 nm) absorption analyzer. Ambient air flows through one absorption cell while air scrubbed of ozone flows through an adjacent one. This allows continuous measurement of both background and absorption signals. Flows are switched between cells by a pair of solenoid valves, which permits monitoring of optical changes. Water vapor is detected with a tunable diode laser spectrometer designed and built by Randy May. This sensor employs a room-temperature near-infrared laser (single mode at about 1.37 microns) and second harmonic detection, rather than direct absorption. Unlike the JPL water instrument, this sensor has an internal absorption path, optimized for the mid-troposphere. Carbon dioxide is measured by its absorption in the infrared (4.25 microns) using a LiCor NDIR instrument. This is also a dual-cell device, in which the absorption caused by the ambient air sample is compared to that from a reference gas of known composition. Halocarbons are monitored with a custom-built gas chromatograph, using short, packed columns and small ovens, and HP micro-electron capture detectors. Ambient sample and standard will be run simultaneously on paired columns to reduce errors associated with drift in ECD response.

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14-channel NASA Ames Airborne Tracking Sunphotometer

AATS-14 measures direct solar beam transmission at 14 wavelengths between 354 and 2139 nm in narrow channels with bandwidths between 2 and 5.6 nm for the wavelengths less than 1640 nm and 17.3 nm for the 2139 nm channel. The transmission measurements at all channels except 940 nm are used to retrieve spectra of aerosol optical depth (AOD). In addition, the transmission at 940 nm and surrounding channels is used to derive columnar water vapor (CWV) [Livingston et al., 2008]. Methods for AATS-14 data reduction, calibration, and error analysis have been described extensively, for example, by Russell et al. [2007] and Shinozuka et al. [2011]. AATS-14 measurements of spectral AOD and CWV obtained during aircraft vertical profiles can be differentiated to determine corresponding vertical profiles of spectral aerosol extinction and water vapor density. Such measurements have been used extensively in the characterization of the horizontal and vertical distribution of aerosol optical properties and in the validation of satellite aerosol sensors. For example, in the Aerosol Characterization Experiment-Asia (ACE-Asia), AATS measurements were used for closure (consistency) studies with in situ aerosol samplers aboard the NCAR C-130 and the CIRPAS Twin-Otter aircraft, and with ground-based lidar systems. In ACE-Asia, CLAMS (Chesapeake Lighthouse & Aircraft Measurements for Satellites, 2001), the Extended-MODIS-λ Validation Experiment (EVE), INTEX-A, INTEX-B, and ARCTAS, AATS results have been used in the validation of satellite sensors aboard various EOS platforms, providing important aerosol information used in the improvement of retrieval algorithms for the MISR and MODIS sensors among others.

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Airborne Scanning Microwave Limb Sounder

The Airborne Scanning Microwave Limb Sounder (A-SMLS) makes wide-swath vertical profile observations of the composition
of the upper troposphere and lower stratosphere (the atmospheric region from ~10–20km altitude). A-SMLS measurements are
well suited to studies of convective outflow, long-range pollution transport, and exchange of air between the
troposphere and stratosphere. These atmospheric processes have strong impacts on climate and air quality but are
currently incompletely understood. Improved understanding of these issues is one of the main goals of NASA’s atmospheric
composition Earth science focus area. A-SMLS airborne observations reflect the priority spaceborne “Ozone and Trace Gas”
observables identified in the recent Decadal Survey.

A-SMLS was initially developed and flown on the WB-57 under the NASA Instrument Incubator Program (IIP), following
which, it was adapted to the ER-2 platform. Subsequent work, funded under an additional IIP, has upgraded the receivers
to ones that require cooling to only 70K rather than the previously needed 4K, and to use newer technology digital
spectrometers. Test flights for A-SMLS in this new configuration are planned, but further work, proposed here, is needed
to make the instrument fully “campaign ready”.

A-SMLS observes a ~300km-wide swath ~300km ahead of the aircraft in a 2D raster scan (azimuth and elevation), with
~10x10km horizontal sampling (across and along-track). As typically configured, A-SMLS measures water vapor, ozone, and
carbon monoxide. Retuning of the instrument (including in flight) can provide measurements of other species (including
N2O, HCN, CH3CN, H2CO, and others).

The instrument would be a particularly valuable addition to multi-aircraft campaigns. The broad swath A-SMLS
observations from the ER-2 could be used in near-real-time to help guide lower altitude aircraft carrying in situ
sensors to regions of interest.

As part of NASA's Airborne Instrument Technology Transition (AITT) program, the instrument is currently being updated to
help cement its suitability for campaign-mode operations, specifically, this involves:

- Addition of a liquid cooling loop to transfer waste heat from the existing ~70K cryocooler to the outer skin of the
ER-2 wing pod.

- Development of an “intelligent scan” system that accounts for aircraft orientation etc. when performing the 2D
raster limb scan on the atmosphere.

- Completion of a thorough ground-based instrument calibration.

- Development of an on-board radiance compression scheme that will enable key data to be transferred to the ground for
use in real-time flight planning as described above.

- Updates to the analysis algorithms software used for Aura MLS, enabling their application to A-SMLS observations.

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WB-57 - JSC (no longer fits), ER-2 - AFRC
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Chemical Ionization Mass Spectrometer

The NOAA chemical ionization mass spectrometer (CIMS) instrument was developed for high-precision measurements of gaseous nitric acid (HNO3) specifically under high- and variable-humidity conditions in the boundary layer. The instrument’s background signals (i.e., signals detected when HNO3-free air is measured), which depend on the humidity and HNO3 concentration of the sample air, are the most important factor affecting the limit of detection (LOD). A new system to provide HNO3-free air without changing both the humidity and the pressure of the sampled air was developed to measure the background level accurately. The detection limit was about 23 parts per trillion by volume (pptv) for 50-s averages. Field tests, including an intercomparison with the diffusion scrubber technique, were carried out at a surface site in Tokyo, Japan, in October 2003 and June 2004. A comparison between the measured concentrations of HNO3 and particulate nitrate indicated that the interference from particulate nitrate was not detectable (i.e., less than about 1%). The intercomparison indicated that the two independent measurements of HNO3 agreed to within the combined uncertainties of these measurements.

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Airborne Earth Science Microwave Imaging Radiometer

The Airborne Earth Science Microwave Imaging Radiometer (AESMIR) is a passive microwave airborne imager covering the 6-100 GHz bands that are essential for observing key Earth System elements such as precipitation, snow, soil moisture, ocean winds, sea ice, sea surface temperature, vegetation, etc.

AESMIR’s channels are configured to enable it to simulate various channels on multiple satellite radiometers, including AMSR-E, SSMI, SSMIS, AMSU, ATMS, TMI, GMI, ATMS, & MIS. Programmable scan modes include conical and cross-track scanning. As such, AESMIR can serve as an inter-satellite calibration tool for constellation missions (e.g., GPM) as well as for long-term multi-satellite data series (Climate Data Records).

The most unique/cutting edge feature of the instrument is its coverage of key water cycle microwave bands in a single mechanical package—making efficient & cost-effective use of limited space on research aircraft, and maximizing the possibilities for co-flying with other instruments to provide synergistic science. State-of-the-art calibration, fully-polarimetric (4-Stokes) observations, and the ability to accommodate large/heavy sensors (up to 300 kg) are other features of AESMIR. AESMIR currently flies on the NASA P-3 aircraft.

With these capabilities, AESMIR is an Earth Science facility for new microwave remote sensing discovery, pre-launch algorithm development, and post-launch Calibration/Validation activities, as well as serving as a technology risk reduction testbed for upcoming spaceborne radiometers. In the latter role, AESMIR is already supporting the GPM, Aquarius, and SMAP missions.

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Airborne Laser Isotope Spectrometer

Isotopic CO2 measurements have been identified as an important component of NASA's Earth Science Enterprise's Carbon Cycle Initiative as part of its program in global climate change. The isotopic composition of atmospheric CO2, and especially its 13CO2/ 12CO2 ratio, is an established tool for understanding the details of the global carbon cycle, since this ratio can distinguish between oceanic and terrestrial biospheric sinks of CO2.

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Aircraft Laser Infrared Absorption Spectrometer

ALIAS (Aircraft Laser Infrared Absorption Spectrometer) measures total water, total water isotopes, carbon monoxide, and carbon dioxide isotope ratios. No other instrument provides real-time measurements of carbon dioxide isotope ratios which are clear identifiers of atmospheric transport (18O/17O/16O for stratospheric intrusion, 13C/12C for anthropogenic signals). ALIAS easily adapts to changing mission priorities and can be configured to measure HCl, CH4, SO2, and N2O by simply replacing a semiconductor laser. These measurements contribute to Atmospheric Composition Focus Area research by providing key data on how convective processes affect stratospheric composition, the development of cirrus particles and their affect on Earth's radiative balance, and health of the ozone layer through measurement of chlorine partitioning.

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