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Robbins, D. E.

Publications and source records attributed to Robbins, D. E..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Response of a tissue equivalent proportional counter to neutrons

The absorbed dose as a function of lineal energy was measured at the CERN-EC Reference-field Facility (CERF) using a 512-channel tissue equivalent proportional counter (TEPC), and neutron dose equivalent response evaluated. Although there are some differences, the measured dose equivalent is in agreement with that measured by the 16-channel HANDI tissue equivalent counter. Comparison of TEPC measurements with those made by a silicon solid-state detector for low linear energy transfer particles produced by the same beam, is presented. The measurements show that about 4% of dose equivalent is delivered by particles heavier than protons generated in the conducting tissue equivalent plastic. c2002 Elsevier Science Ltd. All rights reserved.

NASA Center JSC↗
NASA NTRS1996

Decay rate of the second radiation belt

Variations in the Earth's trapped (Van Allen) belts produced by solar flare particle events are not well understood. Few observations of increases in particle populations have been reported. This is particularly true for effects in low Earth orbit, where manned spaceflights are conducted. This paper reports the existence of a second proton belt and it's subsequent decay as measured by a tissue-equivalent proportional counter and a particle spectrometer on five Space Shuttle flights covering an eighteen-month period. The creation of this second belt is attributed to the injection of particles from a solar particle event which occurred at 2246 UT, March 22, 1991. Comparisons with observations onboard the Russian Mir space station and other unmanned satellites are made. Shuttle measurements and data from other spacecraft are used to determine that the e-folding time of the peak of the second proton belt. It was ten months. Proton populations in the second belt returned to values of quiescent times within eighteen months. The increase in absorbed dose attributed to protons in the second belt was approximately 20%. Passive dosimeter measurements were in good agreement with this value.

Badhwar, G. D.↗
NASA NTRS1989

Measurements of nitric oxide in the stratosphere at 44 N in autumn

Precision of the chemiluminescent instrument for balloon-borne NO measurement was improved by precise determinations of the flow rates of the sample air and the calibration NO in N2 gas. Based on the new calibration of these values, NO mixing ratio in the stratosphere was reanalyzed. The revision of the NO data does not at all alter the form of the diurnal variation. The average of the four NO profiles between 15 and 32 km obtained at 44 N in autumn is given.

Kondo, Y.↗
NASA NTRS1987

Comparison of in situ stratospheric ozone measurements obtained during the MAP/GLOBUS 1983 campaign

Data from five types of in situ ozone sensors flown aboard ballons during the MAP/GLOBUS 1983 campaign were found to agree to within 5 percent uncertainty throughout the middle atmosphere. A description of the individual techniques and the error budget is given in addition to explanations for the discrepancies found at higher and lower altitudes. In comparison to UV photometry values, results from two electrochemical techniques were found to be greater in the lower atmosphere and to be lower in the upper atmosphere. In general, olefin chemiluminescence results were within 8 percent of the UV photometry results. Ozone column contents measured by the indigo colorization technique for two altitude regions of about 6 km height were greater than measurements from other techniques by 52 and 17 percent, respectively.

Aimedieu, P.↗
NASA NTRS1987

General comparison of ozone vertical profiles obtained by various techniques during the 1983 MAP/GLOBUS campaign

As part of the 1983 MAP/GLOBUS campaign, atmospheric ozone profile measurements were made using a large variety of different techniques both from balloon platforms and the ground. It is shown that, for most techniques, the measured height distributions agree to within + or - 5 percent with the exception of the remote visible absorption method. This + or - 5 percent uncertainty is of the order of the individual intersystem accuracy. It is suggested that since the differences with the visible absorption method are in magnitude rather than in form, the absorption cross-section data could be the possible cause for the discrepancy.

Matthews, W. A.↗
NASA NTRS1985

Instrument intercomparisons and assessments

Over the past few years, several field campaigns were devoted to the goal of assessing instrument reliability, as opposed to solely obtaining data to answer a geophysical question. Some examples of the formal instrument intercomparisons that have occurred in the past decade and those that are planned for the very near future are listed chronologically. Balloon-borne techniques and instruments that address the height profiles of the trace species in the lower stratosphere are emphasized. Beginning with the most extensively studied trace constituent, the approach taken and the results obtained, are described. The current status of the measurement capabilities are summarized, and the needs for future intercomparisons and assessments are listed.

Albritton, D. L.↗
NASA NTRS1985

Balloon in-situ measurements of ozone with the NASA-JSC UV photometer

Details of the design and performance of a UV absorption photometer used to measure ozone in the stratosphere from large balloons are given. Mechanisms which might cause a loss of ozone in the instrument are shown to be negligible. An analysis of errors obtains an instrumental precision that is better than 3 percent and an accuracy less than 5 percent. Improvements are being made that will increase the precision to about 1 percent and the accuracy to 3 percent. The NASA-JSC photometer has been intercompared with other techniques during several balloon campaigns. Agreement with other in-situ techniques was usually within 1 to 5 percent, while agreement with remote techniques was typically in the range 10 to 15 percent.

Robbins, D. E.↗
NASA NTRS1983

NASA-JSC measurements during la campagne d'intercomparaison d'ozonometres, Gap, France, June 1981

Measurements made by the NASA-JSC ozone instrument during the ozone intercomparison campaign from Gap, France during June 1981 are reported. Two flights were made on board the large balloon platform with other instruments using different techniques. The NASA-JSC instrument employs UV absorption photometry to obtain in situ results. Concentration and mixing ratio profiles are given for altitudes from 16 km to float altitudes of 32 and 39 km, respectively, for the two flights. A measure of the total column content of ozone was obtained by integrating the NASA-JSC results from 16 km to float altitude and combining them with results from other techniques below 16 km and above float altitudes.

Robbins, D. E.↗
NASA NTRS1983

Ozone profile intercomparison based on simultaneous observations between 20 and 40 km

The vertical distribution of stratospheric ozone has been simultaneously measured by means of five different instruments carried on the same balloon payload. The launches were performed from Gap during the intercomparison campaign conducted in June 1981 in southern France. Data obtained between altitudes of 20 and 40 km are compared and discussed. Vertical profiles deduced from Electrochemical Concentration Cell sondes launched from the same location by small balloons and from short Umkehr measurements made at Mt Chiran (France) are also included in this comparison. Systematic differences of the order of 20 percent between ozone profiles deduced from solar u.v. absorption and in situ techniques are found.

Aimedieu, P.↗
NASA NTRS1982

LIMS Instrument Package (LIP) balloon experiment: Nimbus 7 satellite correlative temperature, ozone, water vapor, and nitric acid measurements

The Limb Infrared Monitor of the Stratosphere (LIMS) LIP balloon experiment was used to obtain correlative temperature, ozone, water vapor, and nitric acid data at altitudes between 10 and 36 kilometers. The performance of the LIMS sensor flown on the Nimbus 7 Satellite was assessed. The LIP consists of the modified electrochemical concentration cell ozonesonde, the ultraviolet absorption photometric of ozone, the water vapor infrared radiometer sonde, the chemical absorption filter instrument for nitric acid vapor, and the infrared radiometer for nitric acid vapor. The limb instrument package (LIP), its correlative sensors, and the resulting data obtained from an engineering and four correlative flights are described.

Lee, R. B., III↗
NASA NTRS1980

NASA-JSC ozone observations for validation of Nimbus 7-LIMS data

A series of balloon flights undertaken to validate data received from the limb infrared monitor of the stratorphere instrument aboard the Nimbus 7 satellite is discussed. Ozone data profiles, which included altitude, pressure, and mixing ratio, obtained during both ascent and descent of the balloons are reported. The measurement concept, instrumental uncertainties, and temporal variations observed for several time periods are discussed.

Robbins, D. E.↗
NASA NTRS1978

Variations in the upper stratosphere's ozone profile

The ozone concentration profile was measured on five balloon flights using an instrument which employs the strong absorption in ultraviolet to measure ozone in situ. Altitudes up to 44 km were obtained. All the flights were made during the daytime except for one that was launched at 3 AM local time to obtain a nighttime profile and to observe sunrise effects. Although the measurements were obtained at different times of day and during different seasons, ozone concentrations in the upper stratosphere varied by only a few percent. Quadratic, least squares fits to the data between 34 km and 40 km for the four daytime flights, yield a mean concentration at 37 km of 1.02 x 10 to the 12th power molecules/cu cm with a 2 percent standard deviation. Measurements made through sunrise show a small increase in ozone at 37 km commencing shortly after the beginning of astronomical twilight. The concentration at 37 km returned to predawn levels about 2 1/2 hours later.

Robbins, D. E.↗
NASA NTRS1976

Comparison of stratospheric ozone destruction by fluorocarbons 11, 12, 21, and 22

Measured photoabsorption cross sections for fluorocarbons (FC) 11, 12, 21, and 22 are presented for the wavelength region from 1740 A to about 2200 A. Solar radiation in this region dissociates these molecules in the stratosphere releasing atomic chlorine which participates in catalytic reactions that destroy ozone. Photolysis by solar UV is the only known loss mechanism for FC11 and FC12. However, FC21, and FC22 also react with OH in the troposphere reducing the amount of ground level releases which reach the stratosphere. Calculations comparing the steady state stratospheric C1X due to equal release rates of fluorocarbons 11, 12, 21, and 22 are presented using a range of OH profiles and eddy diffusion coefficients. These calculations indicate approximately a factor of 20 to 450 less C1X in the stratosphere for FC21 and a factor of 40 to 130 for FC22, compared to an equal release rate of FC11 and FC12.

Robbins, D. E.↗
NASA NTRS1976

Photodissociation of methyl chloride and methyl bromide in the atmosphere

Methyl chloride (CH3Cl) and methyl bromide (CH3Br) have been suggested to be significant sources of the stratospheric halogens. The breakup of these compounds in the stratosphere by photodissociation or reaction with OH releases halogen atoms which catalytically destroy ozone. Experimental results are presented for ultraviolet photoabsorption cross sections of CH3Cl and CH3Br. Calculations are presented of loss rates for the methyl halides due to photodissociation and reaction with OH and of mixing ratios of these species in the stratosphere.

Robbins, D. E.↗
NASA NTRS1974

The helium component of solar wind velocity streams

Systematic variations of the properties of the helium constituent of the solar wind in the velocity streams are described. It is found that the helium abundance varies by about a factor of 2 as the stream is crossed. The velocity of the helium differs from that of the hydrogen by a few kilometers per second throughout much of the stream structure. This velocity difference is greatest immediately after the proton density peak passes, the helium velocity being typically 20 km/sec faster than the protons at that position in the stream. A sharp dip in the helium to proton temperature ratio is centered on the proton density peak. Although it appears reasonable that at least the velocity and temperature effects are due to the dynamic interactions of the two streams, it is not yet clear exactly what physical processes are directly involved in producing the effects described here.

Hirshberg, J.↗