DC-8 - AFRC

The Microwave Temperature Profiler (MTP) is a passive microwave radiometer, which measures the natural thermal emission from oxygen molecules in the earth’s atmosphere for a selection of elevation angles between zenith and nadir. The current observing frequencies are 55.51, 56.65 and 58.80 GHz. The measured "brightness temperatures" versus elevation angle are converted to air temperature versus altitude using a quasi-Bayesian statistical retrieval procedure. The MTP has no ITAR restrictions, has export compliance classification number EAR99/NLR. An MTP generally consists of two assemblies: a sensor unit (SU), which receives and detects the signal, and a data unit (DU), which controls the SU and records the data. In addition, on some platforms there may be a third element, a real-time analysis computer (RAC), which analyzes the data to produce temperature profiles and other data products in real time. The SU is connected to the DU with power, control, and data cables. In addition the DU has interfaces to the aircraft navigation data bus and the RAC, if one is present. Navigation data is needed so that information such as altitude, pitch and roll are available. Aircraft altitude is needed to perform retrievals (which are altitude dependent), while pitch and roll are needed for controlling the position of a stepper motor which must drive a scanning mirror to predetermined elevation angles. Generally, the feed horn is nearly normal to the flight direction and the scanning mirror is oriented at 45-degrees with respect to receiving feed horn to allow viewing from near nadir to near zenith. At each viewing position a local oscillator (LO) is sequenced through two or more frequencies. Since a double sideband receiver is used, the LO is generally located near the "valley" between two spectral lines, so that the upper and lower sidebands are located near the spectral line peaks to ensure the maximum absorption. This is especially important at high altitudes where "transparency" corrections become important if the lines are too "thin." Because each frequency has a different effective viewing distance, the MTP is able to "see" to different distances by changing frequency. In addition, because the viewing direction is also varied and because the atmospheric opacity is temperature and pressure dependent, different effective viewing distances are also achieved through scanning in elevation . If the scanning is done so that the applicable altitudes (that is, the effective viewing distance times the sine of the elevation angle) at different frequencies and elevation angles are the same, then inter-frequency calibration can also be done, which improves the quality of the retrieved profiles. For a two-frequency radiometer with 10 elevation angles, each 15-second observing cycle produces a set of 20 brightness temperatures, which are converted by a linear retrieval algorithm to a profile of air temperature versus altitude, T(z). Finally, radiometric calibration is performed using the outside air temperature (OAT) and a heated reference target to determine the instrument gain. However, complete calibration of the system to include "window corrections" and other effects, requires tedious analysis and comparison with radiosondes near the aircraft flight path. This is probably the most important single factor contributing to reliable calibration. For stable MTPs, like that on the DC8, such calibrations appear to be reliable for many years. Such analysis is always performed before MTP data are placed on mission archive computers.

The Meteorological Measurement System (MMS) is a state-of-the-art instrument for measuring accurate, high resolution in situ airborne state parameters (pressure, temperature, turbulence index, and the 3-dimensional wind vector). These key measurements enable our understanding of atmospheric dynamics, chemistry and microphysical processes. The MMS is used to investigate atmospheric mesoscale (gravity and mountain lee waves) and microscale (turbulence) phenomena. An accurate characterization of the turbulence phenomenon is important for the understanding of dynamic processes in the atmosphere, such as the behavior of buoyant plumes within cirrus clouds, diffusions of chemical species within wake vortices generated by jet aircraft, and microphysical processes in breaking gravity waves. Accurate temperature and pressure data are needed to evaluate chemical reaction rates as well as to determine accurate mixing ratios. Accurate wind field data establish a detailed relationship with the various constituents and the measured wind also verifies numerical models used to evaluate air mass origin. Since the MMS provides quality information on atmospheric state variables, MMS data have been extensively used by many investigators to process and interpret the in situ experiments aboard the same aircraft.

The Center for Remote Sensing of Ice Sheets (CReSIS) has developed radars (MCoRDS) that operate over the frequency range from 140 to 230 MHz with multiple receivers developed for airborne sounding and imaging of ice sheets. MCoRDS radars have an adjustable radar bandwidth of 20 MHz to 60 MHz. Multiple receivers permit digital beamsteering for suppressing cross-track surface clutter that can mask weak ice-bed echoes and strip-map synthetic aperture radar (SAR) images of the ice-bed interface. With 200 W of peak transmit power, a loop sensitivity > 190 dB is achieved. These radars are flown on twin engine and long-range aircraft including NASA P-3 and DC-8.

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 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 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.

A modified LI-COR model 6252 infrared gas analyzer forms the basis of a CO2 sampling system. The LI-COR is small (13 x 24 x 34 cm) and composed of dual 12 cm3 volume sample/reference cells; a feedback stabilized infrared source; 500 Hz chopper; thermoelectrically-cooled solid state PbSe detector; and a narrow band (150 nm) interference filter centered on the 4.26 μm CO2 absorption band. Using synchronous signal detection techniques, it operates by sensing the difference in light absorption between the continuously flowing sample and reference gases occupying each side of the dual absorption cell. Thus, by selecting a reference gas of approximately the same concentration as background air (~ 378 ppmv), very minute fluctuations in atmospheric concentration can be quantified with high precision (≤ 0.07 ppmv). The system is operated at constant pressure (250 torr) and has a 0.1 second electronic time response.

During ambient sampling, air is continuously drawn through a Rosemount inlet probe, a permeable membrane dryer to remove H2O(v), the LI-COR, and then exchanged through a diaphragm pump that vents overboard. In-flight calibrations are performed every 15 minutes using standards traceable to the primary standards maintained by the WMO Central CO2 Laboratory. By interpolating between these calibrations, slow drifts in instrument response are effectively suppressed, yielding high precision values. Temperature control of the instrument minimizes thermal drift thus maximizing ambient sampling time by decreasing calibration frequency. The CO2 measurement accuracy is closely tied to the accuracy of the standards obtained from NOAA/CMDL, Boulder, CO prior to the mission.

NASA’s Land, Vegetation and Ice Sensor (LVIS) is a wide-swath, high-altitude, full-waveform airborne laser altimeter and camera sensor suite designed to provide elevation and surface structure measurements over hundreds of thousands of square kilometers. LVIS is an efficient and cost-effective capability for mapping land, water, and ice surface topography, vegetation height and vertical structure, and surface dynamics. The LVIS Facility is comprised of two high-altitude scanning lidar systems plus cameras that have been integrated on numerous NASA, NSF, and commercial aircraft platforms providing a diverse and flexible capability to meet a broad range of science needs. The newest Facility lidar (LVIS-F) began operations in 2017 using a 4,000 Hz laser, and an earlier 1,000 Hz sensor built in 2010 has undergone various upgrades (LVIS-Classic). High-resolution, commercial off-the-shelf cameras are co-mounted with LVIS lidars providing geotagged image coverage across the LVIS swath. LVIS sensors have flown extensively for a wide range of science applications and have been installed on over a dozen different aircraft, most recently on NASA’s high-altitude Gulfstream-V jet based at Johnson Space Center

The LVIS lidars are full-waveform laser altimeters, meaning that the systems digitally record both the outgoing and reflected laser pulse shapes providing a true 3-dimensional record of the surface and centimeter-level range precision. Multiple science data products are available for each footprint, including the geolocated waveform vector, sub-canopy topography, canopy or structure height, surface complexity, and others. LVIS lidars map a ±6 degree wide data swath centered on nadir (e.g., at an operating altitude of 10 km, the data swath is 2 km wide). They are designed to fly at higher altitudes than what is typical for commercial lidars in order to map a wider swath with low incidence angles, avoid the need for terrain following, while operating at much higher speeds that maximize the range of the aircraft. Recent data campaigns include deployments to Antarctica, Greenland, Canada, Alaska, the conterminous US, Central America, French Guiana, and Gabon.

The LIP (Lightning Instrument Package) measures lightning, electric fields, electric field changes, air conductivity. LIP provides real time electric field data for science and operations support.

The LIP is comprised of a set of optical and electrical sensors with a wide range of temporal, spatial, and spectral resolution to observe lightning and investigate electrical environments within and above thunderstorms. The instruments provide measurements of the air conductivity and vertical electric field above thunderstorms and provide estimates of the storm electric currents. In addition, LIP will detect total storm lightning and differentiate between intracloud and cloud-to-ground discharges. This data is used in studies of lightning/storm structure and lightning precipitation relationships.