Design and Performance of a High-Stability Water Vapor Radiometer

[1] The design of two new high-stability microwave water vapor radiometers is presented along with a performance evaluation. The radiometers operate next to a spacecraft tracking station at NASA's Goldstone facility in California, where they will be used to calibrate tropospheric path delay fluctuations during an upcoming gravity-wave search experiment (GWE) involving the Cassini spacecraft. Observing frequencies of the radiometers are 22.2, 23.8, and 31.4 GHz, and the antenna beam width is 1°. The instruments are room temperature Dicke radiometers with additive noise injection for gain calibration. Design highlights include: (1) a practical temperature control system capable of stabilizing the entire receiver to a few millikelvin from day to night; (2) redundant noise diode injection circuits with 30 ppm RF power stability; and (3) a voice coil actuated waveguide vane attenuator which is used as a high-performance Dicke switch. Performance of the radiometers is evaluated from intercomparisons of the two radiometers and from continuous tip curve calibrations spanning nearly 1 year. Structure function analysis of the intercomparison data indicates that the brightness temperature stability of these radiometers is better than 0.01 K on 1000-10,000 s timescales. Analysis of tip curve calibrations indicates RMS errors of $0.05 K on 30-day timescales and 0.15 K on 1-year timescales

Robust array configuration for a microwave interferometric radiometer: application to the geoSTAR project

The Geostationary Synthetic Thinned Array Radiometer represents a promising new approach to microwave atmospheric sounding from geostationary orbit based on passive interferometry. One of the major concerns about the feasibility of this new concept is related to the ability of the sensor to cope with the failure of one or several of its single receivers/antennas. This letter shows that the inclusion of a small percentage of additional antennas significantly reduces the degradation of radiometric resolution caused by such receiver failure. Impact of antenna failure is analyzed, taking into account two test images with very different spatial harmonic content. A tradeoff analysis of several array topologies is performed so as to minimize the number of additional antennas while keeping worst case radiometric error within a reasonable level.Peer Reviewe

Single-Antenna Temperature- and Humidity-Sounding Microwave Receiver

For humidity and temperature sounding of Earth s atmosphere, a single-antenna/LNA (low-noise amplifier) is needed in place of two separate antennas for the two frequency bands. This results in significant mass and power savings for GeoSTAR that is comprised of hundreds of antennas per frequency channel. Furthermore, spatial anti-aliasing would reduce the number of horns. An anti-aliasing horn antenna will enable focusing the instrument field of view to the hurricane corridor by reducing spatial aliasing, and thus reduce the number of required horns by up to 50 percent. The single antenna/receiver assembly was designed and fabricated by a commercial vendor. The 118 183-GHz horn is based upon a profiled, smooth-wall design, and the OMT (orthomode transducer) on a quad-ridge design. At the input end, the OMT presents four ver y closely spaced ridges [0.0007 in. (18 m)]. The fabricated assembly contains a single horn antenna and low-noise broadband receiver front-end assembly for passive remote sensing of both temperature and humidity profiles in the Earth s atmosphere at 118 and 183 GHz. The wideband feed with dual polarization capability is the first broadband low noise MMIC receiver with the 118 to 183 GHz bandwidth. This technology will significantly reduce PATH/GeoSTAR mass and power while maintaining 90 percent of the measurement capabilities. This is required for a Mission-of-Opportunity on NOAA s GOES-R satellite now being developed, which in turn will make it possible to implement a Decadal-Survey mission for a fraction of the cost and much sooner than would otherwise be possible

Sources and characteristics of summertime organic aerosol in the Colorado Front Range: perspective from measurements and WRF-Chem modeling

Abstract. The evolution of organic aerosols (OAs) and their precursors in the boundary layer (BL) of the Colorado Front Range during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ, July–August 2014) was analyzed by in situ measurements and chemical transport modeling. Measurements indicated significant production of secondary OA (SOA), with enhancement ratio of OA with respect to carbon monoxide (CO) reaching 0.085±0.003 µg m−3 ppbv−1. At background mixing ratios of CO, up to  ∼  1.8 µg m−3 background OA was observed, suggesting significant non-combustion contribution to OA in the Front Range. The mean concentration of OA in plumes with a high influence of oil and natural gas (O&G) emissions was  ∼  40 % higher than in urban-influenced plumes. Positive matrix factorization (PMF) confirmed a dominant contribution of secondary, oxygenated OA (OOA) in the boundary layer instead of fresh, hydrocarbon-like OA (HOA). Combinations of primary OA (POA) volatility assumptions, aging of semi-volatile species, and different emission estimates from the O&G sector were used in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) simulation scenarios. The assumption of semi-volatile POA resulted in greater than a factor of 10 lower POA concentrations compared to PMF-resolved HOA. Including top-down modified O&G emissions resulted in substantially better agreements in modeled ethane, toluene, hydroxyl radical, and ozone compared to measurements in the high-O&G-influenced plumes. By including emissions from the O&G sector using the top-down approach, it was estimated that the O&G sector contributed to  <  5 % of total OA, but up to 38 % of anthropogenic SOA (aSOA) in the region. The best agreement between the measured and simulated median OA was achieved by limiting the extent of biogenic hydrocarbon aging and consequently biogenic SOA (bSOA) production. Despite a lower production of bSOA in this scenario, contribution of bSOA to total SOA remained high at 40–54 %. Future studies aiming at a better emissions characterization of POA and intermediate-volatility organic compounds (IVOCs) from the O&G sector are valuable

Circulating CD34+ Cell Count is Associated with Extent of Subclinical Atherosclerosis in Asymptomatic Amish Men, Independent of 10-Year Framingham Risk

Background Bone-marrow derived progenitor cells (PCs) may play a role in maintaining vascular health by actively repairing damaged endothelium. The purpose of this study in asymptomatic Old Order Amish men (n = 90) without hypertension or diabetes was to determine if PC count, as determined by CD34+ cell count in peripheral blood, was associated with 10-year risk of cardiovascular disease (CVD) and measures of subclinical atherosclerosis. Methods and Results CD34+ cell count by fluorescence-activated cell sorting, coronary artery calcification (CAC) by electron beam computed tomography, and CVD risk factors were obtained. Carotid intimal-medial thickness (CIMT) also was obtained in a subset of 57 men. After adjusting for 10-year CVD risk, CD34+ cell count was significantly associated with CAC quantity ( p =0.03) and CIMT ( p < 0.0001). A 1-unit increase in natural-log transformed CD34+ cell count was associated with an estimated 55.2% decrease (95% CI: −77.8% to −9.3%) in CAC quantity and an estimated 14.3% decrease (95% CI: −20.1% to −8.1%) in CIMT. Conclusions Increased CD34+ cell count was associated with a decrease in extent of subclinical atherosclerosis in multiple arterial beds, independent of 10-year CVD risk. Further investigations of associations of CD34+ cell count with subclinical atherosclerosis in asymptomatic individuals could provide mechanistic insights into the atherosclerotic process

Miniature Low-Noise G-Band I-Q Receiver

Weather forecasting, hurricane tracking, and atmospheric science applications depend on humidity sounding of atmosphere. Current instruments provide these measurements from groundbased, airborne, and low Earth orbit (LEO) satellites by measuring radiometric temperature on the flanks of the 183-GHz water vapor line. Miniature, low-noise receivers have been designed that will enable these measurements from a geostationary, thinned array sounder, which is based on hundreds of low-noise receivers that convert the 180-GHz signal directly to baseband in-phase and in-quadrature signals for digitization and correlation. The developed receivers provide a noise temperature of 450 K from 165 to 183 GHz (NF = 4.1 dB), and have a mass of 3 g while consuming 24 mW of power. These are the most sensitive broadband I-Q receivers at this frequency range that operate at room temperature, and are significantly lower in mass and power consumption than previously reported receivers

High-Altitude MMIC Sounding Radiometer for the Global Hawk Unmanned Aerial Vehicle

Microwave imaging radiometers operating in the 50-183 GHz range for retrieving atmospheric temperature and water vapor profiles from airborne platforms have been limited in the spatial scales of atmospheric structures that are resolved not because of antenna aperture size, but because of high receiver noise masking the small variations that occur on small spatial scales. Atmospheric variability on short spatial and temporal scales (second/ km scale) is completely unresolved by existing microwave profilers. The solution was to integrate JPL-designed, high-frequency, low-noise-amplifier (LNA) technology into the High-Altitude MMIC Sounding Radiometer (HAMSR), which is an airborne microwave sounding radiometer, to lower the system noise by an order of magnitude to enable the instrument to resolve atmospheric variability on small spatial and temporal scales. HAMSR has eight sounding channels near the 60-GHz oxygen line complex, ten channels near the 118.75-GHz oxygen line, and seven channels near the 183.31-GHz water vapor line. The HAMSR receiver system consists of three heterodyne spectrometers covering the three bands. The antenna system consists of two back-to-back reflectors that rotate together at a programmable scan rate via a stepper motor. A single full rotation includes the swath below the aircraft followed by observations of ambient (roughly 0 C in flight) and heated (70 C) blackbody calibration targets located at the top of the rotation. A field-programmable gate array (FPGA) is used to read the digitized radiometer counts and receive the reflector position from the scan motor encoder, which are then sent to a microprocessor and packed into data files. The microprocessor additionally reads telemetry data from 40 onboard housekeeping channels (containing instrument temperatures), and receives packets from an onboard navigation unit, which provides GPS time and position as well as independent attitude information (e.g., heading, roll, pitch, and yaw). The raw data files are accessed through an Ethernet port. The HAMSR data rate is relatively low at 75 kbps, allowing for real-time access over the Global Hawk high-data-rate downlink. Once on the ground, the raw data are unpacked and processed through two levels of processing. The Level 1 product contains geo-located, time-stamped, calibrated brightness temperatures for the Earth scan. These data are then input to a lD variational retrieval algorithm to produce temperature, water vapor, and cloud liquid water profiles, as well as several derived products such as potential temperature and relative humidity

Atmospheric Acetaldehyde: Importance of Air-Sea Exchange and a Missing Source in the Remote Troposphere.

We report airborne measurements of acetaldehyde (CH3CHO) during the first and second deployments of the National Aeronautics and Space Administration (NASA) Atmospheric Tomography Mission (ATom). The budget of CH3CHO is examined using the Community Atmospheric Model with chemistry (CAM-chem), with a newly-developed online air-sea exchange module. The upper limit of the global ocean net emission of CH3CHO is estimated to be 34 Tg a-1 (42 Tg a-1 if considering bubble-mediated transfer), and the ocean impacts on tropospheric CH3CHO are mostly confined to the marine boundary layer. Our analysis suggests that there is an unaccounted CH3CHO source in the remote troposphere and that organic aerosols can only provide a fraction of this missing source. We propose that peroxyacetic acid (PAA) is an ideal indicator of the rapid CH3CHO production in the remote troposphere. The higher-than-expected CH3CHO measurements represent a missing sink of hydroxyl radicals (and halogen radical) in current chemistry-climate models

Signals for CPT and Lorentz Violation in Neutral-Meson Oscillations

Experimental signals for indirect CPT violation in the neutral-meson systems are studied in the context of a general CPT- and Lorentz-violating standard-model extension. In this explicit theory, some CPT observables depend on the meson momentum and exhibit diurnal variations. The consequences for CPT tests vary significantly with the specific experimental scenario. The wide range of possible effects is illustrated for two types of CPT experiment presently underway, one involving boosted uncorrelated kaons and the other involving unboosted correlated kaon pairs.Comment: Accepted in Physical Review D, scheduled for December 1999 issu