Engineering topics

Brown, C. A., Jr.

Publications and source records attributed to Brown, C. A., Jr..

At least 19 records

NASA NTRS1983

Visible absorbance spectra: A basis for in situ and passive remote sensing of phytoplankton concentration and community composition

The concentration and composition of phytoplankton populations are measured by an optical method which can be used either in situ or remotely. This method is based upon the in vivo light absorption characteristics of phytoplankton. To provide a data base for testing assumptions relative to the proposed method, visible absorbance spectra of pure cultures of 20 marine phytoplankton were obtained under laboratory conditions. Descriptive and analytical statistics were computed for the absorbance spectra and were used to make comparisons between members of major taxonomic groups and between groups. Spectral variation between the members of the major taxonomic groups was observed to be considerably less than the spectral variation between these groups. In several cases the differences between the mean absorbance spectra of major taxonomic groups are significant enough to be detected with passive remote sensing techniques.

Farmer, F. H.↗

NASA NTRS1981

Analysis of ALOPE data from Superflux

Remote sensing data collected with the airborne lidar oceanographic probing experiment (ALOPE) laser fluorosensor during the Superflux 1 and Superflux 2 experiments were analyzed using two techniques. A qualitative technique which requires no supplementary data provided a near-real-time estimate of relative abundance of the golden-brown and green phytoplankton color groups. Contour plots developed for the later mission are used to demonstrate the utility of this technique. A quantitative technique which requires supplementary data to define the attenuation coefficient provides chlorophyll a concentration by color group. The sum of the golden-brown and green chlorophyll a data yields total chlorophyll a values which may be compared with in situ data. As expected, the golden-brown population was dominant in the Chesapeake Bay and the Bay plume whereas the green population was dominant in shelf waters.

Jarrett, O., Jr.↗

NASA NTRS1981

Laboratory tank studies of a single species of phytoplankton using a remote sensing fluorosensor

Phytoplankton were grown in the laboratory for the purpose of testing a remote fluorosensor. The fluorosensor uses a unique four-wavelength dye laser system to excite phytoplankton bearing chlorophyll and to measure the chlorophyll fluorescence generated by this excitation. Six different species were tested, one at a time, and each was grown two to four times. Fluorescence measured by the fluorosensor provides good quantitative measurement of chlorophyll concentrations for all species tested while the cultures were in log phase growth. Fluorescene cross section ratios obtained in the single species tank tests support the hypothesis that the shape of the fluorescence cross section curve remains constant with the species (differences in fluorescence cross section ratios are a basis for determining composition of phytoplankton according to color group when a multiwavelength source of excitation is used. Linear relationships exist between extracted chlorophyll concentration and fluorescence measured by the remote fluorosensor during the log phase growth of phytoplankton cultures tested.

Brown, C. A., Jr.↗

NASA NTRS1979

Remote sensing of phytoplankton density and diversity in Narragansett Bay using an airborne fluorosensor

An aircraft-borne remote system is presented that utilizes narrow-band light from multiple dye lasers to excite selected algae photopigments and then measures the resultant flourescence emitted from chlorophyll a at 685 nm. Tests were conducted with both pure and mixed cultures of marine algae from a series of field tests taken from piers and bridges of Narragansett Bay, and a prototype remote fluorosensor was flown over the Bay during the 1978 winter-spring diatom bloom. Remote fluorescence obtained at hover points over sea-truth stations showed correlations with in situ fluorescence, total chlorophyll a, and cell count. It was concluded that the ratio of remote fluorescence to direct chlorophyll a concentration was less variable than expected, and the distribution of total chlorophyll a between two major photoplankton color groups showed three distinct areas, within the Bay, of green and golden-brown species.

Farmer, F. H.↗

NASA NTRS1979

Measurement of chlorophyll a fluorescence with an airborne fluorosensor

Phytoplankton biomass and diversity among various algal species are important for marine productivity assessments. The spatial heterogeneity of phytoplankton in coastal and estuarine environments complicates estimates of total biomass using conventional surface sampling techniques. Since synoptic or near-synoptic data can be quite useful in these studies, this area is a natural focal point for development of remote sensors. However, it is very difficult to sense phytoplankton density and diversity with spacecraft-borne passive sensors primarily because modulation in the signal due to phytoplankton is of the same order as that of atmospheric effects. The same sensors mounted on aircraft may be able to detect and quantify high concentrations of phytoplankton (blooms), but the current lack of knowledge about the spectral reflectance signatures of the major phytoplankton color groups rules out any diversity measurements by this type of sensor. An active fluorosensor mounted on a low-flying aircraft or helicopter is not limited by any of these constraints. A brief survey of the four currently active systems is presented.

Jarrett, O., Jr.↗

NASA NTRS1978

Laboratory studies of in vivo fluorescence of phytoplankton

A lidar system is developed that uses four selected excitation wavelengths to induce chlorophyll 'a' fluorescence which is indicative of both the concentration and diversity of phytoplankton. The operating principles of the system and the results of measurements of phytoplankton fluorescence in a controlled laboratory environment are presented. A comparative study of results from lidar fluorosensor laboratory tank tests using representative species of phytoplankton in single and multispecies cultures from each of four color groups reveals that (1) there is good correlation between the fluorescence of chlorophyll 'a' remotely simulated and detected by the lidar system and in-situ measurements using four similar excitation wavelengths in a flow-through fluorometer; (2) good correlation exists between the total chlorophyll 'a' calculated from lidar-fluorosensor data and measurements obtained by the Strickland-Parsons method; and (3) the lidar fluorosensor can provide an index of population diversity.

Brown, C. A., Jr.↗

NASA NTRS1975

Multiwavelength LIDAR for remote sensing of chlorophyll A in algae and phytoplankton

A theoretical and experimental analysis of laser induced fluorescence for remote detection of chlorophyll A in living algae and phytoplankton is presented. The fluorescent properties of various species of algae representative of the different color groups are described. Laboratory measurements of fluorescent scattering cross sections is discussed and quantitive data presented. A scattering matrix model is developed to demonstrate the essential requirement of multiwavelength laser excitation in order to make accurate quantitative measurements of chlorophyll A concentration when more than one color group of algae is present in the water. A practical airborne laser fluorosensor design is considered and analysis of field data discussed. Successful operation of the Langley ALOPE (airborne LIDAR oceanographic probing experiment) system is described and field measurements presented. Accurate knowledge of alpha, the optical attenuation coefficient of the water, is shown to be essential for quantitative analysis of chlorophyll A concentration. The feasibility of remotely measuring alpha by laser radar is discussed.

Mumola, P. B.↗

NASA NTRS1974

A new approach to mass spectrometer measurements of thermospheric density

The gas sampling problem in satellite and high velocity probes was investigated by applying the theory of a drifting Maxwellian gas. A lens system using a free stream ion source was developed and experimentally evaluated over the pressure range of 0.00001 to 0.01 N/m sq (approx. 10 to the minus 7th power to 0.0001 torr). The source has high beam transparency, which minimizes gas-surface collisions within, or near, the ionization volume. It is shown that for high ion energy (60 eV), the extracted ion beam has an on-axis energy spread of less than 4 eV, and that 90 percent of the ions are within 2.5 deg of the beam axis. It is concluded that the molecular beam mass spectrometer concept, developed for gas density measurements in the upper atmosphere, substantially reduces gas-surface scattering and gas-surface reactions in the sample, and preserves the integrity of the gas sample during the analysis process. Studies show that both the Scout and Delta launch vehicles have adequate volume, control, velocity, and data acquisition capability necessary to obtain thermospheric number density in real time.

Melfi, L. T., Jr.↗

NASA NTRS1974

Effects of Reynolds number and model support on the supersonic aerodynamic chacteristics of a 140 deg-included-angle cone

An investigation has been made in the Langley Unitary Plan wind tunnel to determine the effects of Reynolds number and sting-support interference on the static aerodynamic characteristics of a 140 deg-included-angle cone. Base pressures and forces and moments of the model were measured at Mach numbers of 1.50, 2.00, 2.94, and 4.00 for ratios of sting diameter to model diameter that varied from 0.125 to 0.500 through an angle-of-attack range from about minus 4 deg to 13 deg. The Reynolds number, based on model diameter 4.80 in. was varied from 161,000 to 415,000.

Trescot, C. D., Jr.↗

NASA NTRS1973

Experimental wake survey behind Viking 75 entry vehicle at angles of attack of 0 deg, 5 deg, and 10 deg, Mach numbers from 0.20 to 1.20, and longitudinal stations from 1.50 to 11.00 body diameters

An investigation was conducted to obtain flow properties in the wake of a preliminary configuration of the Viking '75 Entry Vehicle at Mach numbers from 0.20 to 1.20 and at angles of attack of 0 deg, 5 deg, and 10 deg. The wake flow properties were calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.50 to 11.00 body diameters, and are presented in tabulated and plotted form. The wake properties were essentially symmetrical about the X-axis at alpha = 0 deg and the profiles were shifted away from the X-axis at angles of attack. An unexpected reduction in wake property ratios occurred as the Mach number increased from 0.60 to 1.00; these ratios then increased as the Mach number increased to 1.20. The reduction was present for all the longitudinal stations of the tests and decreased with increased longitudinal distance.

Brown, C. A., Jr.↗

NASA NTRS1973

Dye laser remote sensing of marine plankton

Dye laser, emitting four wavelengths sequentially in time, has been incorporated into helicopter-borne lidar flight package, for performing studies of laser-induced fluorescence of chlorophyll A in algae. Data obtained by multicolor lidar technique can provide water-resource management with rapid-access wide-area coverage of the impact of various environmental factors for any body of water.

Mumola, P. B.↗

NASA NTRS1973

Evaluation of experimental flow properties in the wake of a Viking '75 entry vehicle.

An experimental investigation has been conducted to obtain the flow properties in the wake of a model of the Viking '75 entry vehicle. Data are presented for the model at several angles of attack at free-stream Mach numbers from 0.2 to 3.95. The characteristics of the wake flow field are discussed and results are shown to demonstrate the significant variation of wake center-line flow properties in the transonic speed range, the shift in wake profiles with change in angle of attack, and the similarity exhibited by the velocity profiles across the wake.

Campbell, J. F.↗

NASA NTRS1973

Evaluation of flow properties behind 120 deg and 140 deg included-angle cones and a Viking 1975 entry vehicle at Mach numbers from 1.60 to 3.95

The flow properties in the wake of 120 degree and 140 degree included angle cones and a model of the preliminary configuration of the Viking 75 entry vehicle were evaluated. Wake flow properties were calculated from total and static pressures measured with a pressure-survey rake. Data are presented for free stream Mach numbers from 1.60 to 3.95, longitudinal stations from 1.0 to 8.39 body diameters downstream of the maximum diameter, and vertical stations from plus 1.04 to minus 1.04 body diameters measured from the wake center line for an angle of attack of zero degrees.

Brown, C. A., Jr.↗

NASA NTRS1973

Four wavelength lidar applied to determination of chlorophyll a concentration and algae color group

A technique for remote measurement of chlorophyll a density and determination of algae color group is described. In vivo fluorescence measurements of chlorophyll a for four color groups of algae (green, golden-brown, red, and blue-green) are described, and representative spectra are shown. The lidar equation is developed for the general case of a mixture of color groups showing the need for multicolor excitation. The lidar instrument which has been designed and fabricated at Langley Research Center for helicopter flights over surrounding portions of the Chesapeake Bay is described. The lidar package contains a unique four-color dye laser which permits multicolor excitation of chlorophyll a fluorescence from the various color groups of algae.

Jarrett, O., Jr.↗

NASA NTRS1973

Multiwavelength laser induced fluorescence of algae in-vivo - A new remote sensing technique

In order to accurately determine the quantity of chlorophyll a in living algae by fluorescence spectrometry, either remotely or in the laboratory, the fluorescence excitation cross section must be known. Laboratory fluorescence studies of a number of different algae species representative of the various color groups were performed. These measurements indicate distinct maximum spectral excitation regions which differ from one color group to another. Within each color group, however, the fluorescent properties were nearly identical, regardless of species. These two key features - namely, the similarity of fluorescent properties within a color group, and the distinct spectral differences between color groups - make possible the simultaneous determination of chlorophyll a content of an unknown mixture of phytoplankton and the distribution of chlorophyll a among the various color groups.

Mumola, P. B.↗

NASA NTRS1972

Experimental aerodynamic characteristics of 120 deg included-angle cone with attached and separated 20 deg included-angle cone at Mach numbers of 2.36 and 2.70

An investigation has been conducted in a unitary plan wind tunnel to determine the aerodynamic characteristics of two different size blunt 120 deg-included-angle cones behind a 20 deg-included-angle cone. Forces and moments were measured at Mach numbers of 2.36 and 2.70, longitudinal separation distances from 0 to 3.5 body diameters, lateral (side) distances from 0 to 0.50 body diameter, angles of attack of the 120 deg-included-angle cone from 0.5 deg to 22 deg, angles of attack of the 20 deg-included-angle cone from 0 deg to 180 deg, and a Reynolds number of one million per foot. Large variations in pitching-moment, normal-force, and axial-force coefficients were noted for both Mach numbers and all longitudinal distances for the 120 deg cones in the wake of a 20 deg cone.

Brown, C. A., Jr.↗

NASA NTRS1971

Experimental wake survey behind a 140 deg-included-angle cone at angles of attack of 0 deg and 5 deg, Mach numbers from 1.60 to 3.95, and longitudinal stations varying from 1.0 to 8.39 body diameters

The flow properties in the wake of a 140 deg-included-angle cone at Mach numbers from 1.60 to 3.95 and at angles of attack of 0 deg and 5 deg are discussed. The wake flow properties are calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.0 to 8.39 body diameters and at lateral stations varying from -0.42 to 3.0 body diameters. These measurements show a consistent trend throughout the range of Mach number and longitudinal distance and an increase in dynamic pressure with increasing longitudinal station.

Brown, C. A., Jr.↗

NASA NTRS1971

Experimental wake survey behind Viking 1975 entry vehicle at angles of attack of 0 deg and 5 deg, Mach numbers from 1.60 to 3.95, and longitudinal stations from 1.0 to 8.39 body diameters

An investigation was conducted to obtain flow properties in the wake of the Viking '75 entry vehicle at Mach numbers from 1.60 to 3.95 and at angles of attack of 0 deg and 5 deg. The wake flow properties were calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.0 to 8.39 body diameters and lateral stations varying from -0.42 to 3.0 body diameters. These measurements showed a a consistent trend throughout the range of Mach numbers and longitudinal distances and an increase in dynamic pressure with increasing downstream position.

Brown, C. A., Jr.↗