NASA - National Aeronautics and Space Administration

COBALT makes measurements using off-axis integrated output spectroscopy.

The CO2LAS instrument was jointly developed by JPL and Lockheed Martin Coherent Technologies under funding from the NASA Earth Science Technology Office Instrument Incubator Program.

The instrument uses three continuous-wave (c.w.) Th:Ho:YLF lasers, one of which is used as an absolute frequency reference and is locked to a carbon dioxide absorption line in an internal gas cell using a phase modulation spectroscopy scheme. The remaining two lasers are offset frequency locked from the reference laser to provide the online and offline beams that are propagated through the atmosphere. The online and offline beams are expanded to an eye-safe level and transmitted to the ground where they are reflected back to the instrument, collected by the receive optics and detected. The use of the offset frequency-locking scheme together with the absolute frequency reference enables the absolute frequency of the online and offline lasers to be held to within 200 kHz of the desired values. The CO2LAS transceiver uses separate co-axial transmit/receive paths for each of the on-line and off-line channels.

A Doppler frequency shift is induced between the outgoing and return signals by pointing the transmit beams slightly off nadir. This frequency offset, together with a polarization transmit/receive architecture, ensures the receive signals are separated from the transmit signals by both polarization and frequency. The nominal Doppler offset is 15 MHz but this will vary as the aircraft attitude changes. The return signals on each channel are digitized and stored during flight for post-processing. Throughput of the data collection system was increased from ~8% to >20% between 2006 and 2007.

In order to ensure the instrument remains stable, the output power and frequency of all three lasers are monitored. The output power values for the online and offline lasers are used in the determination of the on-line and off-line absorption as part of the LAS measurement. The output power value for the reference laser is used primarily as a laser health status to check the integrity of the CO2 line center lock.

The electronics for the CO2LAS are mounted in two racks that typically mount to the seat rails of the host aircraft. One rack contains the control electronics for the transceiver system, laser controller, frequency locking electronics and provides the user interface for the overall system.

The second rack houses the chiller that supplies the optical transceiver with coolant and the signal processor which receives housekeeping data from the electronics rack, and digitizes, stores and analyzes the lidar return signal. The CO2LAS uses a Gigabit Ethernet system to distribute data across the system and to other computers that can be connected into the gigabit hub located in the back of one of the racks.

The CNC counts particles in the approximate diameter range from 0.006 m to 2 m. The instrument operates by exposing the articles to saturated Flourinert vapor at 28 C and then cooling the sample in a condenser at 5 C. The supersaturation of the vapor increases as it is cooled and the vapor condenses on the particles causing them to grow to sizes which are easily detected. The resulting droplets are passed through a laser beam and the scattered light is detected. Individual particles are counted and are referred to as condensation nuclei (CN). Two CN Counters are provided in the instrument. One counts the particles after sampling from the atmosphere and the second counts particles that have survived heating to 192C. Lab experiments show that pure sulfuric acid particles smaller than 0.05 mm are volatilized in the heater. The heated channel detects when small particles are volatile and permits speculation about the composition. The CNC II contains an impactor collector which permits the collection of particles on electron microscope grids for later 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 collect efficiently even at small Reynolds numbers. The system collects particles as small as 0.02 m at WB-57 cruise altitudes. As many as 25 samples can be collected in a flight.

The University of Colorado closed-path tunable diode laser hygrometer (CLH) is based on the water vapor hygrometers designed by R. D. May (Maycomm, Inc.). CLH is coupled to a heated, forward-facing inlet that enhances particulate water by anisokinetic sampling. Ice water content (IWC) is derived from the measurement of enhanced total water, with knowledge of the instrument sampling characteristics, particle size distributions and ambient water vapor.

In contrast to the open-path systems of similar heritage, the CLH, which was designed for operation in the troposphere on commercial aircraft, has a single-pass absorption cell (27.62 cm long). The light source is a room-temperature solid-state laser that puts out 3-5 mW of radiation at 1.37 mm (7306.752 cm-1).

CIP obtains cloud particle images using a 64-element photodiode array probe to generate 2-Dimensional images of particles from 25-1550 μm, as well as sizing in 1-Dimensional histogram form, and includes housekeeping data.

The CIN-100A is designed for aircraft mounting and measures the optical extinction coefficient and asymmetry parameter.

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.

The single mass analyzer CIMS (S-CIMS) was developed for use on NASA’s ER-2 aircraft. Its first measurements were made in 2000 (SOLVE, see photo). Subsequently, it has flown on the NASA DC-8 aircraft for INTEX-NA, DICE, TC4, ARCTAS, ATom, KORUS, FIREX, as well as on the NCAR C-130 during MILAGRO/INTEX-B. HNO3 is measured by selective ion chemical ionization via the fluoride transfer reaction: CF3O^- + HNO3 → HF • NO3^- + CF2O In addition to its fast reaction rate with HNO3, CF3O^- can be used to measure additional acids and nitrates as well as SO2 [Amelynck et al., 2000; Crounse et al., 2006; Huey et al., 1996]. We have further identified CF3O^- chemistry as useful for the measurement of less acidic species via clustering reactions [Crounse et al., 2006; Paulot et al., 2009a; Paulot et al., 2009b; St. Clair et al., 2010]: CF3O^- + HX → CF3O^- • HX where, e.g., HX = HCN, H2O2, CH3OOH, CH3C(O)OOH (PAA) The mass analyzer of the S-CIMS instrument was first upgraded from a quadrupole to a unit-mass resolution time-of-flight (ToF) analyzer. In 2023, the mass filter was again upgraded to an 1m flight path (~5000 deltaM/M).  The ToF admits the sample ion beam to the ion extractor, where a pulse of high voltage orthogonally deflects and accelerates the ions into the reflectron, which in turn redirects the ions toward the multichannel plate detector. Ions in the ToF follow a V-shaped from the extractor to detector, separating by mass as the smaller ions are accelerated to greater velocities by the high voltage pulse. The detector collects the ions as a function of time following each extractor pulse. The rapid-scan collection of the ToF guarantees a high temporal resolution (1 Hz or faster) and simultaneous data products from the S-CIMS instrument for all mass channels [Drewnick et al., 2005]. We have flown a tandem CIMS (TCIMS) instrument in addition to the SCIMS since INTEX-B (2006). The T-CIMS provides parent-daughter mass analysis, enabling measurement of compounds precluded from quantification by the S-CIMS due to mass interferences (e.g. MHP) or the presence of isobaric compounds (e.g. isoprene oxidation products) [Paulot et al., 2009b; St. Clair et al., 2010]. Calibrations of both CIMS instruments are performed in flight using isotopically-labeled reagents evolved from a gas cylinders or from a thermally-stabilized permeation tube oven [Washenfelder et al., 2003]. By using an isotopically labeled standard, the product ion signals are distinct from the natural analyte and calibration can be performed at any time without adversely affecting the ambient measurement.