NASA Goddard Space Flight Center Research Articles

Raman Lidar Measurements during the International H2O Project. Part I: Instrumentation and Analysis Techniques

Abstract The NASA Goddard Space Flight Center (GSFC) Scanning Raman Lidar (SRL) participated in the International H2O Project (IHOP), which occurred in May and June 2002 in the midwestern part of the United States. The SRL received extensive optical modifications prior to and during the IHOP campaign that added new measurement capabilities and enabled unprecedented daytime water vapor measurements by a Raman lidar system. Improvements were also realized in nighttime upper-tropospheric water vapor measurements. The other new measurements that were added to the SRL for the IHOP deployment included rotational Raman temperature, depolarization, cloud liquid water, and cirrus cloud ice water content. In this first of two parts, the details of the operational configuration of the SRL during IHOP are provided along with a description of the analysis and calibration procedures for water vapor mixing ratio, aerosol depolarization, and cirrus cloud extinction-to-backscatter ratio. For the first time, a Raman water vapor lidar calibration is performed, taking full account of the temperature sensitivity of water vapor and nitrogen Raman scattering. Part II presents case studies that permit the daytime and nighttime error statistics to be quantified.

Using TRMM/TMI to Retrieve Surface Soil Moisture over the Southern United States from 1998 to 2002

Abstract Passive microwave remote sensing has been recognized as a potential method for measuring soil moisture. Combined with field observations and hydrological modeling brightness temperatures can be used to infer soil moisture states and fluxes in real time at large scales. However, operationally acquiring reliable soil moisture products from satellite observations has been hindered by three limitations: suitable low-frequency passive radiometric sensors that are sensitive to soil moisture and its changes; a retrieval model (parameterization) that provides operational estimates of soil moisture from top-of-atmosphere (TOA) microwave brightness temperature measurements at continental scales; and suitable, large-scale validation datasets. In this paper, soil moisture is retrieved across the southern United States using measurements from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) X-band (10.65 GHz) radiometer with a land surface microwave emission model (LSMEM) developed by the authors. Surface temperatures required for the retrieval algorithm were obtained from the Variable Infiltration Capacity (VIC) hydrological model using North American Land Data Assimilation System (NLDAS) forcing data. Because of the limited information content on soil moisture in the observed brightness temperatures over regions characterized by heavy vegetation, active precipitation, snow, and frozen ground, quality control flags for the retrieved soil moisture are provided. The resulting retrieved soil moisture database will be available through the NASA Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC) at a 1/8° spatial resolution across the southern United States for the 5-yr period of January 1998 through December 2002. Initial comparisons with in situ observations obtained from the Oklahoma Mesonet resulted in seasonal correlation coefficients exceeding 0.7 for half of the time covered by the dataset. The dynamic range of the satellite-derived soil moisture dataset is considerably higher compared to the in situ data. The spatial pattern of the TMI soil moisture product is consistent with the corresponding precipitation fields.

Intra-satellite networking

Aerospace remote-sensing payloads are continuing to advance to higher speeds and increasing the demands of on-board intra-satellite networks. These payloads include synchronous continuous mode and asynchronous event-driven sensor data requiring real-time transfer with deterministic latency to capture sensor data. The networked satellite payloads include combinations of: uplinks, downlinks, sensors, processors, formatters, storage devices (recorders), and payload controller. Advanced systems planned for development in the next few years require data rates of 1–10 Gbps. An effective aerospace data-handling network must supply real-time data that is fault tolerant and able to withstand the rigorous conditions of launch as well as the harsh space environment. The IEEE1393-1999 Standard for spaceborne fibre-optic data bus (SFODB) has established the design requirements for the interconnection of these on-board aerospace subsystems. Programs involving NASA Goddard Space Flight Center, the Air Force Research Laboratories, Space Photonics Incorporated, the University of Arkansas, and others, are in the process of developing components necessary for the implementation of the SFODB. SFODB utilizes fibre-optic components for subsystem interconnect and eliminates cable-to-cable and box-to-box EMI, significant reductions in size, weight, and power are among the achievable characteristics that are desirable for aerospace applications. This paper discusses SFODB characteristics and the status of implementation programs. Copyright © 2006 John Wiley & Sons, Ltd.

Victor R. Basili's contributions to software quality

This article deals with Victor R. Basili's contributions to software quality. Basili's contributions cover three broad areas: research in the 1970s and early 1980s on software measurement and the Goal Question Metric (GQM) model, research in the 1980s and 1990s on these measurement ideas' maturation into a software engineering model of empirical studies, including the development of the Quality Improvement Paradigm (QIP) and the influence of the NASA Goddard Space Flight Center Software Engineering Laboratory, and research since 1990 in the Experience Factory as a model for creating learning organizations for continuous software process improvement. Some of Basili's most important contributions are in measuring software development processes and products and gifted the community with an invaluable tool: the GQM approach. The GQM approach is based on the assumption that for an organization to measure its products and processes usefully, it must first specify goals for itself and its projects

Diagnostics of the large‐scale mixing properties from stratospheric analyses

We present diagnostics of the large‐scale mixing of stratospheric flows for January 2000 using meteorological analyses produced by the GEOS‐3 system of the Data Assimilation Office (DAO) at NASA Goddard Space Flight Center (GSFC), the European Centre for Medium‐Range Weather Forecasts (ECMWF), and the Met Office (METO). To characterize the mixing properties of these numerical weather prediction (NWP) systems we calculate diffusion coefficients, contour lengthening rates, and equivalent mixing lengths. Qualitatively, our results show relatively good agreement between the mixing parameters in the upper troposphere and lower stratosphere and reveal similar zones of weak and strong mixing in the middle and upper stratosphere. These parameters, however, exhibit substantial quantitative differences in the middle and upper stratosphere. For January 2000, averaged values for the northern hemisphere (NH) show that the GEOS‐3 and ECMWF flows have strong mixing capabilities while the METO winds result in relatively weak mixing and strong transport polar barriers.

Cryogenic characterization and testing of magnetically-actuated microshutter arrays for the James Webb Space Telescope

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (∼35 K) spectrographic astronomy measurements at near-infrared wavelengths. Functioning as a focal plane object selection device, the MSA is a 2D programmable aperture mask with fine resolution, high efficiency and high contrast. The MSA are close-packed silicon nitride shutters (cell size of 100 µm × 200 µm) patterned with a torsion flexure to allow their opening to 90°. A layer of magnetic material is deposited onto each shutter to permit magnetic actuation. Two electrodes are deposited, one onto each shutter and another onto the support structure side-wall, permitting electrostatic latching and 2D addressing. New techniques were developed to test MSA under mission-similar conditions (8 K ⩽ T < 300 K). The ‘magnetic rotisserie’ has proven to be an excellent tool for rapid characterization of MSA. Tests conducted with the magnetic rotisserie method include accelerated cryogenic lifetesting of unpackaged 128 × 64 MSA and parallel measurement of the magneto-mechanical stiffness of shutters in ‘pathfinder’ test samples containing multiple MSA designs. Lifetest results indicate a logarithmic failure rate out to ∼106 shutter actuations. These results have increased our understanding of failure mechanisms and provide a means to predict the overall reliability of MSA devices.

Influence of isentropic transport on seasonal ozone variations in the lower stratosphere and subtropical upper troposphere

The isentropic cross‐tropopause ozone transport has been estimated in both hemispheres in 1999 based on the potential vorticity mapping of Stratospheric Aerosol and Gas Experiment II ozone measurements and contour advection calculations using the NASA Goddard Space Flight Center Global and Modeling Assimilation Office analysis. The estimated net isentropic stratosphere‐to‐troposphere ozone flux is ∼118 ± 61 × 109 kg yr−1 globally within the layer between 330 and 370 K in 1999; 60% of it is found in the Northern Hemisphere, and 40% is found in the Southern Hemisphere. The monthly average ozone fluxes are strongest in summer and weakest in winter in both hemispheres. The seasonal variations of ozone in the lower stratosphere (LS) and upper troposphere (UT) have been analyzed using ozonesonde observations from ozonesonde stations in the extratropics and subtropics, respectively. It is shown that observed ozone levels increase in the UT over subtropical ozonesonde stations and decrease in the LS over extratropical stations in late spring/early summer and that the ozone increases in the summertime subtropical UT are unlikely to be explained by photochemical ozone production and diabatic transport alone. We conclude that isentropic transport is a significant contributor to ozone levels in the subtropical upper troposphere, especially in summer.

Ground Validation for the Tropical Rainfall Measuring Mission (TRMM)

Abstract An overview of the Tropical Rainfall Measuring Mission (TRMM) Ground Validation (GV) Program is presented. This ground validation (GV) program is based at NASA Goddard Space Flight Center in Greenbelt, Maryland, and is responsible for processing several TRMM science products for validating space-based rain estimates from the TRMM satellite. These products include gauge rain rates, and radar-estimated rain intensities, type, and accumulations, from four primary validation sites (Kwajalein Atoll, Republic of the Marshall Islands; Melbourne, Florida; Houston, Texas; and Darwin, Australia). Site descriptions of rain gauge networks and operational weather radar configurations are presented together with the unique processing methodologies employed within the Ground Validation System (GVS) software packages. Rainfall intensity estimates are derived using the Window Probability Matching Method (WPMM) and then integrated over specified time scales. Error statistics from both dependent and independent validation techniques show good agreement between gauge-measured and radar-estimated rainfall. A comparison of the NASA GV products and those developed independently by the University of Washington for a subset of data from the Kwajalein Atoll site also shows good agreement. A comparison of NASA GV rain intensities to satellite retrievals from the TRMM Microwave Imager (TMI), precipitation radar (PR), and Combined (COM) algorithms is presented, and it is shown that the GV and satellite estimates agree quite well over the open ocean.

A new perspective on Earth

A NASA‐funded scientist has produced the first detailed image of Earth radiating gamma rays, the agency announced on 24 March.Dirk Petry of the NASA Goddard Space Flight Center in Greenbelt, Maryland, assembled the image from seven years worth of data from NASA's Compton Gamma‐Ray Observatory, which was active from 1991 to 2000.

Hurricane forecasting with the high‐resolution NASA finite volume general circulation model

A high‐resolution finite volume general circulation model (fvGCM), resulting from a development effort of more than ten years, is now being run operationally at the NASA Goddard Space Flight Center and Ames Research Center. The model is based on a finite volume dynamical core with terrain‐following Lagrangian control volume discretization and performs efficiently on massive parallel architectures. The computational efficiency allows simulations at a resolution of a quarter of a degree, which is double the resolution currently adopted by most global models in operational weather centers. Such fine global resolution brings us closer to overcoming a fundamental barrier in global atmospheric modeling for both weather and climate, because tropical cyclones can be more realistically represented. In this work, preliminary results are shown. Fifteen simulations of four Atlantic tropical cyclones in 2002 and 2004, chosen because of varied difficulties presented to numerical weather forecasting, are performed. The fvGCM produces very good forecasts of these tropical systems, adequately resolving problems like erratic track, abrupt recurvature, intense extratropical transition, multiple landfall and reintensification, and interaction among vortices.

The STEREO mission: an overview

In February 2006, NASA will launch the twin STEREO spacecraft from Kennedy Space Center aboard a Delta 7925 launch vehicle. After a series of highly eccentric Earth orbits with apogees beyond the moon, each spacecraft will use close flybys of the moon to escape into heliocentric orbits at 1 AU, with one spacecraft trailing Earth and the other leading Earth. As viewed from the Sun, the two spacecraft will separate at approximately 45° per year. The purposes of the STEREO Mission are to understand the causes and mechanisms of coronal mass ejection initiation and to follow the propagation of CMEs through the heliosphere. Additionally, STEREO will study the mechanisms and sites of energetic particle acceleration and develop 3D time-dependent models of the magnetic topology, temperature, density and velocity of the solar wind between the Sun and Earth. To accomplish these goals, each STEREO spacecraft will be equipped with a set of optical, radio and in situ particles and fields instruments. The SECCHI suite of instruments includes two white light coronagraphs covering the range from 1.4 to 15 solar radii, an extreme ultra violet imager covering the chromosphere and inner corona, and two heliospheric white light imagers covering the outer corona from 12 solar radii to 1 AU. The IMPACT suite of instruments will measure in situ solar wind electrons in the energy range from essentially 0 to 100 keV, energetic electrons to 6 MeV, and protons and heavier ions to 100 MeV/nucleon. IMPACT also contains a magnetometer to measure the in situ magnetic field strength and direction. The PLASTIC instrument will measure the composition of heavy ions as well as protons and alpha particles. The SWAVES instrument will use radio waves to track the location of CME-driven shocks and the 3D topology of open field lines along which energetic particles flow. Additionally, SWAVES will measure in situ plasma waves to provide an independent estimate of the local plasma density and temperature. Each of the four instruments will produce a small real-time stream of selected data for purposes of predicting space weather events at Earth, primarily for NOAA forecasters. In addition to the four instrument teams, there will be substantial participation by modeling and theory oriented teams. All STEREO data will be freely available through individual Web sites at the four Principal Investigator institutions as well as at the STEREO Science Center located at NASA Goddard Space Flight Center.

Low/medium density biomass, coastal and ocean carbon: a carbon cycle mission

As part of the Global Carbon Cycle research effort, an agency-wide planning initiative was organized between October 2000 and June 2001 by the NASA Goddard Space Flight Center at the behest of the Associate Administrator for Earth Science. The goal was to define future research and technology development activities needed for implementing a cohesive scientific observation plan. A timeline for development of missions necessary to acquire the selected new measurements was laid out, and included missions for low–medium density terrestrial biomass/coastal ocean, and global ocean carbon. This paper will begin with the scientific justification and measurement requirements for these specific activities, lightly touch on the options for having separate low Earth orbiting missions, and follow-up in more detail with a combined implementation study centered on a hyperspectral imager at geosynchronous altitudes, highlighting both its merits and challenges.

Separating chemistry and transport effects in two‐dimensional models

Representation of transport in numerical models is known to be a major uncertainty in modeling of the atmosphere. Models also differ in their treatment of gas phase and heterogeneous chemistry. This paper will describe a quantitative approach to diagnosing the source of intermodel differences in ozone assessment calculations. Our approach is applied to diagnosing the differences between two‐dimensional (2‐D) models from Atmospheric and Environmental Research, the NASA Goddard Space Flight Center, and the Lawrence Livermore National Laboratory. Surprisingly, we find that differences due to chemical formulation are often as large as those due to transport, despite the fact that all models use the same set of reaction rate coefficients. These differences are particularly large when polar stratospheric cloud (PSC) processes are included in the models, though differences due to photolysis rates and details of the sulfate chemistry are also apparent. Perturbation calculations for a scenario including supersonic commercial aircraft operating in the 2015 stratosphere reveal that differences in the accumulation of H2O and NOy emitted by aircraft are due almost entirely to transport, while differences in ozone due to chemical formulation are evident in the lower stratosphere even without differences in H2O and NOy and without PSCs. By demonstrating a capability of separating transport and chemical differences, it is hoped that the results described in this paper will stimulate analogous studies with other models and will thus lead to a deeper understanding of intermodel similarities and differences, along with a means to quantify uncertainties in model predictions of atmospheric response to perturbations.

High‐Resolution Observations of Methyl Cyanide (CH3CN) toward the Hot Core Regions W51e1/e2

$^{a}$ Current address: NASA Goddard Space Flight Center, Earth and Space Data Computing Division, Code 930, Greenbelt, MD 20771 $^{b}$ Current address: Institute of Astronomy and Astrophysics, Acedemia Sinica, P.O. Box 23-141, Taipei 106, Taiwan, R.O.C. $^{c}$ Current address: Purple Mountain Observatory, National Astronomical Observatories, Chinese Academy of Sciences, China

Programmable Microshutter Arrays for the JWST NIRSpec: Optical Performance

Two-dimensional microshutter arrays (MSAs) are being developed at the NASA Goddard Space Flight Center for the James Webb Space Telescope (JWST) for use as a programmable aperture mask for object selection for the Near Infrared Multiobject Spectrograph (NIRSpec). The MSAs are designed to provide high transmission efficiency for the selected objects and high on to off contrast ratio at the /spl sim/35 K operating temperature of JWST. The arrays of shutters are produced from silicon nitride membranes on a 100/spl times/200 /spl mu/m pitch. Individual shutters consist of a shutter blade of silicon nitride suspended from the shutter frame by a nitride torsion flexure. The shutters are normally closed. All shutters in the array are opened by the scanning magnetic field, and are held open by an electrostatic potential applied between the open shutters and the shutter support grid electrodes. To close the required shutters for a specific configuration, the potential between the shutter to be deselected and the support frame is set to zero, allowing the shutter to close. In this way, full random access addressing is achieved. We have produced such shutters and have demonstrated mechanical actuation and selection. Optical tests of open and closed shutters have demonstrated the required contrast for the JWST application. The MSA is a pioneering technology that provides the most capable possible multiobject spectrograph for JWST. It provides high contrast selection, high transmission efficiency, and can meet the environmental requirements for JWST.

In a Mechanism Far, Far Away

This article describes features of James Webb Space Telescope, which is going to take the place of the Hubble Space Telescope in 2011. The Webb telescope is an orbiting infrared observatory, and the project is managed by the NASA Goddard Space Flight Center in Greenbelt, Maryland. The Webb Space Telescope will use extremely large aperture, low-mass mirrors. Made in segments so they can be folded to fit into a rocket nose cone for flight, they will open and array themselves when they reach their destination. These robust mirrors must be fabricated rapidly and cost-effectively. There are significant manufacturing challenges in the composite backplanes for the primary mirror. These are to be made from boron composites for their stiffness. The analysis and manufacturing challenges in the backplane are the adhesives used to combine all the composite parts and the uniformity to which the composites themselves can be manufactured. The structure of the primary mirror for the Webb Telescope permits small adjustments.

Temperature Dependence of the Rate Constant for the Reaction F(2P) + Cl2 → FCl + Cl at T = 180−360 K

The absolute rate constant for the reaction F(2P) with Cl2 has been measured using the discharge flow kinetics technique coupled to mass spectrometric detection at T = 180−360 K and 1 Torr He nominal pressure. Experiments were performed at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD, and Laboratoire de Combustion et Systemes Reactifs-CNRS in Orleans, France. Results of k = (5.7 ± 0.8) × 10-11 and (6.2 ± 0.8) × 10-11 cm3 molecule-1 s-1 independent of temperature were obtained by each laboratory, respectively. When the results from both laboratories were combined into one data set, an average temperature independent value of k1 = (6.0 ± 1.1) × 10-11 cm3 molecule-1 s-1 was obtained. A very slight positive temperature dependence with k1(T) = (6.5 ± 1.5) × 10-11 exp{−(20 ± 60)/T} cm3 molecule-1 s-1 may also be derived from the combined data in the range T = 180−360 K.

De La Beaujardiére receives 2003 Charles S. Falkenberg Award

“Jeff de La Beaujardière received his B.A. in physics in 1985 from the University of California, Berkeley and his Ph.D. in astrophysics in 1990 from the University of Colorado, Boulder. Captivated by the Web's potential for information distribution, in 1994 he joined the NASA Goddard Space Flight Center, first as a contractor and then as a civil servant. He is currently with the Geospatial Interoperability Office in NASA's Earth Science Applications Division.“From 1994 to 1998, Jeff was Webmaster of NASA's Public Use of Remote Sensing Data Program, whose unofficial motto was ‘Data to the people.’ The Web site was a showcase for satellite images of hurricanes and other natural phenomena. He was also lead Web developer for the GLOBE Visualization project, which displays environmental data gathered and used by a worldwide network of students, teachers, and scientists.

Application of ionospheric topside‐sounding results to magnetospheric physics and astrophysics

A brief review is presented to illustrate how the knowledge and experience gained from investigations of ionospheric topside‐sounder ionograms has benefited scientific research beyond the ionosphere. In particular, to the interpretation of (1) natural radio emissions from space plasmas, (2) sounder‐stimulated echoes and plasma emissions, and plasma diagnostics in planetary magnetospheres and (3) X‐ray spectra of disks around neutron stars and black holes. The relevant data are from 60 satellite years of ionospheric topside‐sounder operations by the four satellites of the International Satellites for Ionospheric Studies (ISIS) program from 1963 through 1989. Not all of these data were reduced to ionograms on 35‐mm film. An ongoing effort at the NASA Goddard Space Flight Center is producing digital topside‐sounder ionograms directly from a selected subset of the original telemetry tapes. More than 300,000 digital ionograms are now in the National Space Science Data Center at the NASA GSFC (http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html).

An overview of the SeaWiFS project and strategies for producing a climate research quality global ocean bio-optical time series

Abstract The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project Office was formally initiated at the NASA Goddard Space Flight Center in 1990. Seven years later, the sensor was launched by Orbital Sciences Corporation under a data-buy contract to provide 5 years of science quality data for global ocean biogeochemistry research. To date, the SeaWiFS program has greatly exceeded the mission goals established over a decade ago in terms of data quality, data accessibility and usability, ocean community infrastructure development, cost efficiency, and community service. The SeaWiFS Project Office and its collaborators in the scientific community have made substantial contributions in the areas of satellite calibration, product validation, near-real time data access, field data collection, protocol development, in situ instrumentation technology, operational data system development, and desktop level-0 to level-3 processing software. One important aspect of the SeaWiFS program is the high level of science community cooperation and participation. This article summarizes the key activities and approaches the SeaWiFS Project Office pursued to define, achieve, and maintain the mission objectives. These achievements have enabled the user community to publish a large and growing volume of research such as those contributed to this special volume of Deep-Sea Research. Finally, some examples of major geophysical events (oceanic, atmospheric, and terrestrial) captured by SeaWiFS are presented to demonstrate the versatility of the sensor.