Photometric Field Research Articles

The Temporal Relationship Between Terrestrial Gamma-Ray Flashes and Associated Optical Pulses From Lightning.

We present 221 Terrestrial Gamma‐ray Flashes (TGFs) and associated optical pulses observed by the Atmosphere‐Space Interactions Monitor (ASIM) on board the International Space Station. The events were detected between the end of March 2019 and November 2020 and consist of X‐ and gamma‐ray energy detections, as well as photometer data (180–230, 337, and 777 nm) and optical camera data (337 and 777 nm). Using the available ASIM data and applying a consistency check based on TGF characteristics and lightning detections from lightning radio atmospherics close in time, we determine the most likely position of the TGFs in relation to the photometer field of view (FoV), and the association to the observed optical pulses. Out of the 221 events we find 72 events where the TGF and optical data are determined to be associated and inside the photometer FoV. Using the measured TGF durations and the time between the onsets of the TGFs and optical pulses we find: (a) That the TGF onsets are always before or at the same time as the optical pulse onsets (taking into account cloud scattering). (b) A tendency for longer duration TGFs to have longer delays between onsets. (c) Two groups of events: (a) where there is a possible overlap between the TGFs and the optical emissions, as the TGFs last longer than the delay between onsets and (b) where the TGFs and optical emissions do not overlap, as there are long delays between the onsets, which cannot be explained by cloud scattering.

Evaluation of a method to derive ionospheric conductivities using two auroral emissions (428 and 630\xa0nm) measured with a photometer at Troms\xf8 (69.6\xb0N)

This paper mainly aims at evaluating capabilities of derivation of ionospheric conductivities using two principal auroral emissions (427.8 and 630 nm). We have evaluated a photometric method of derivation of ionospheric conductivities based on simultaneous observations of a photometer (field of view = ~1.2°), a digital camera, and the EISCAT UHF radar (field of view = ~0.7°) operated at Tromsø, Norway (69.6°N, 19.2°E), for two nights on October 10 and 11, 2002. We have compared height-integrated Pedersen and Hall conductivities with a post-integration time of 10 s derived from EISCAT UHF radar observations and photometer observations with wavelengths of 427.8 and 630.0 nm. Sky images taken with the digital camera are utilized for distinguishing types of auroras in the views of the EISCAT UHF radar and the photometer. In general, a good agreement of temporal variations of the height-integrated Pedersen and Hall conductivities was found between EISCAT and photometer values. In cases of auroral arcs passing by in the field of view, however, differences in derived values between the two methods were found. Possible causes of the differences are discussed. We conclude that (1) the photometric method using 427.8 and 630 nm can capture temporal variations of the conductivities well, but unavoidable underestimations of the Pedersen (about 30–40%) and the Hall (about 50–60%) conductivities are involved, and (2) care is necessary for using photometric observational data when auroral arcs appear in the field of view.Graphical .

Integral Field Spectroscopy with Herschel PACS

PACS (Poglitsch et al. [2]) was a photometer and integral field spectrograph (IFS) operating in the FIR (50–220 μm), aboard the ESA-NASA Herschel Space Observatory (Pilbrat et al. [1]). It was the first IFS ever on a space telescope. Herschel operated from May 2009 until April 2013, when its coolant ran out and after which it was sent off in a wide orbit around the sun. In this poster we discuss the importance of the spatial sampling of the PACS beam.

Retrieval of cirrus properties by Sun photometry: A new perspective on an old issue

Cirrus clouds are important modulators of the Earth radiation budget and continue to be one of the most uncertain components in weather and climate modeling. Sun photometers are widely accepted as one of the most accurate platforms for measuring clear sky aerosol optical depth (AOD). However, interpretation of their measurements is ambiguous in the presence of cirrus. Derivation of a valid AOD under cirrus conditions was focused previously on correction factors, rather than on derivation of cirrus cloud optical thickness (COT). In the present work, we propose a new approach that uses the total measured irradiance to derive cirrus COT and ice particle effective diameter (Deff). For this approach, we generate lookup tables (LUTs) of total transmittance for the Sun photometer field of view (FOV) due to the direct and scattered irradiance over the spectral range of 400–2200 nm, for a range of cirrus COT (0–4), and a range of ice cloud effective diameters (10–120 µm) by using explicit cirrus optical property models for (a) cirrus only and (b) a two‐component model including cirrus and aerosols. The new approach is tested on two cases (airborne and ground‐based) using measured transmittances from the 14‐channel NASA Ames Airborne Tracking Sun photometer. We find that relative uncertainties in COT are much smaller than those for Deff. This study shows that for optically thin cirrus cases (COT < 1.0), the aerosol layer between the instrument and the cloud plays an important role, especially in derivation of Deff. Additionally, the choice of the cirrus model may introduce large differences in derived Deff.

Ideal 3D asymmetric concentrator

Nonimaging optics is a field devoted to the design of optical components for applications such as solar concentration or illumination. In this field, many different techniques have been used for producing reflective and refractive optical devices, including reverse engineering techniques. In this paper we apply photometric field theory and elliptic ray bundles method to study 3D asymmetric – without rotational or translational symmetry – concentrators, which can be useful components for nontracking solar applications. We study the one-sheet hyperbolic concentrator and we demonstrate its behaviour as ideal 3D asymmetric concentrator.

Linear Moving-Detector Photometer: A New Design Concept

Current luminaire photometry is relied on using the rotating-mirror or the rotating-detector photometers. While these photometers offer great flexibility and speed in acquiring intensity data in the field around the luminaire, the fact that they use a predefined detector-distance with a fixed incident-angle has demonstrated to be a constraint for the real world applications. The paper presents a new design concept of photometric data acquisition system, Linear Moving-Detector Photometer. This photometry methodology performs the intensity measurements at various distances and at different incident-angles relative to the luminaire in three-dimensional space by using a computer controlled moving-detector system. The photo-detector travels a wide range of distances from a few inches to many feet in a three-dimensional field surrounding the luminaire. It then acquires photometry at the desired locations and orientations. For a typical application, thousands of measurement data can be collected and stored in the computer database. This allows luminous flux and intensity to be reported in both spherical and Cartesian coordinate systems as are required by the specific lighting applications. Actual illuminance distribution on any surfaces in this photometric field can be generated. While linear moving-detector photometer system was not developed to replace existing photometry equipment, this automated equipment will supplement and enhance current photometry methodology.

Radiometric properties of two-aperture fields

A method is described for determining the photometric field given by an extended source when the source is constrained to radiate through two spaced apertures. It is based on a generalization of the photometric inverse-square law in which flux density is considered to be the scalar product of a vector and the unit normal at a given surface element. The result includes an in-plane field that makes the solution independent of element orientation. Computer-generated field maps are used to illustrate the properties of both fields for an arbitrary system. The normal component exhibits two distinct axial inverse-square laws, and the method correctly predicts that total normal flux is conserved on the surfaces considered. Analogous procedures on the in-plane field give new results that complement those of the present scalar theory. Two-aperture effects are commonly found in optical systems. They affect photometric measurements made on or with such systems.

Determination of myoglobin-diffusivity in intact skeletal muscle fibers. An improved microscope-photometrical approach.

In concepts of oxygen transport to muscle tissue an important contribution of myoglobin-facilitated oxygen diffusion to the intracellular oxygen transport is frequently assumed (Wittenberg and Wittenberg, 1990). However, there is lack of direct evidence for a corresponding high diffusivity of myoglobin in intact muscle cells. Jürgens et al. (1990) were the first to present a method to measure the intracellular diffusion coefficient of myoglobin in mammalian muscle fibers. It is based on transmission spectroscopy of dissected and superfused rat diaphragms. In geometrically defined microscopic areas of such samples, photooxidation of oxymyoglobin is performed by short UV pulses. The observed absorbance change at 420 nm, which is subsequently recorded with a computer equipped microscope photometer (Fig.1), is the consequence of the translational myoglobin diffusion along the fiber axes. Metmyoglobin diffuses out of the photometric field while oxymyoglobin enters it simultaneously. KeywordsIrradiate FieldIntracellular OxygenFrog Muscle FiberFrog Skeletal Muscle FiberIntact Muscle CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Inversion techniques for recovering two-dimensional distributions of auroral emission rates from tomographic rocket photometer measurements

In this paper we demonstrate how the spatial distribution of optical emission rates within an auroral arc may be recovered from rocket photometer measurements made in a tomographic spin scan mode. We describe the tomographic inversion procedures required to recover this information and the implementation of two inversion algorithms that are particularly well suited for dealing with the problem of noise in the observational data. These algorithms are based upon the algebraic reconstruction technique and utilize "least-squares" and "maximum-probability" iterative relaxation methods. The performance of the inversion algorithms and the limitations of the rocket tomography technique are assessed using various sets of simulated rocket measurements that were generated from "known" auroral emission-rate distributions. The simulations are used to investigate how the quality of the tomographic recovery may be influenced by various factors such as noise in the data, rocket penetration of the auroral form, background sources of emission, smearing due to the photometer field of view, and temporal variations in the auroral form.

The influence of the aperture of illumination on the accuracy of microscope‐photometric measurements of internal transmittance

SUMMARYThe conical shape of the bundle of illuminating rays in the microscope causes a systematic error of transmittance measured with a microscope photometer in comparison with the (true) transmittance measured with a macrophotometer in which the ray bundle is cylindrical. The error is evaluated by the ratio of transmittance measured with the microscope photometer to the true transmittance. It is calculated for the following model objects: parallel‐sided plates, wedges, spheres and circular cylinders. The results of calculations show that the error increases with decreasing transmittance, increasing angle of the cone of rays (evaluated by the effective numerical aperture of illumination), and increasing relative size of photometric field. On the whole, the error can be neglected if the true internal transmittance is greater than 0.1 (10%), the numerical aperture is less than 0.45 and the radius of the photometric field (in the object plane) is less than one‐fifth of the thickness of the object.

Comment on the Papers “On the influx of small comets into the Earth's upper atmosphere I. Observations and II. Interpretation”

The Generic Screening Object hypothesis of Frank et al. (1986) is refuted, and it is indicated that the DE-1 dark pixel events do not serve as evidence for a large cometary influx. It is shown that the average scan line count profiles of the dark pixel events show no significant reductions in the two neighboring pixel positions, although at least a 9 percent reduction would be expected if the dark pixels were the result of shielding of the photometric field of view. In a reply, Frank et al. uphold their previous hypothesis, pointing out that the suggestion that the atmospheric holes are not a geophysical phenomenon is incorrect due to: (1) the use of an overly simplified model for the instrument responses to small, opaque objects as seen against a statistically fluctuating screen of dayglow intensities; and (2) an insufficient treatment of the observations.

Correlated observations of the equatorward diffuse auroral boundary

The equatorward boundary of the diffuse auroral zone, as viewed via the 6300‐Å (O(¹D)) emission line, has been examined by using ground‐based photometer data. These observations are supplemented with in situ measurements of ionospheric parameters by satellite‐borne instrumentation within the photometer field of view. We find high spatial correlation among 6300‐Å emission, low‐energy (E <1 keV) electron precipitation, and the high‐latitude recovery of ambient electron density which constitutes the poleward cliff of the main ionospheric trough. Time resolution afforded by this ground‐based optical method is especially suited for monitoring the ionospheric signature of this low‐energy particle precipitation over broad longitudes. A model is developed of the statistical equatorward boundary of the diffuse aurora as a function of magnetic local time and magnetic activity (as monitored by Kp index). The local time dependence of this boundary exhibits a latitudinal morphology similar to that of the earthward equatorial plasma sheet—that is, asymmetric about local midnight and skewed toward lesser invariant latitude values within the morning sector.

Error analysis of multi-wavelength sun photometry

The error terms involved in precision multi-wavelength sun photometry, as used to study atmospheric aerosols, are analyzed. The error terms treated include instrumental errors, calibration errors, and errors imposed by the atmosphere. It is shown that in order to derive accurate aerosol parameters, one must exercise great care in the photometer calibration. A procedure for accurate calibration is described, based on an intercalibration between extrapolations of the extraterrestrial solar spectral irradiance and irradiance of a standard lamp. Methods are described to assess, and reduce, uncertainties brought about by diffuse radiation in the photometer's field of view, temporal variations in aerosol optical depth, and gaseous absorption features at the operating wavelength. It is shown that if care is taken sun photometry can be used to derive monochromatic aerosol optical depth to an accuracy of several thousandths.

An automatic method for viability assay of cultured cells.

An automatic method for viability assay of a population of cells is described. Cell populations are stained with trypan blue (for dead cells) and fluorescein diacetate (for live cells). A rapid cell spectrophotometer measures changes in light intensity which occur when individual cells pass through the photometric field. Tallies of the number of decreases (absorption and scatter by dead cells) and the number of increases (fluorescence by live cells) in light intensity are recorded and viability percentages are calculated. These automatically determined viability percentages are compared with viability percentages determined by visual counting and classifying of cells from the same populations.

Luminance matching functions

Three or more different stimuli may be arranged in a photometer field to produce two spectrally different lights which match in luminosity at all levels. A monochromatic stimulus may be so matched by a characteristic mixture of two instrumental stimuli, the quantities of which for a unit test stimulus may be defined as the spectral stimulus values. The set of these values constitutes the luminance matching functions, which may be manipulated algebraically in order to predict the approximate stimulus values of any test light of known constitution. V′ (λ) and V (λ) may be derived as linear transforms of the functions, from mesopic data. Applications to practical photometry are suggested.

A PULSAR HUNTER: TESTS ON NP 0532

Photoelectric photometiy has been employed in many attempts to discover optical counterparts for radio pulsars. The techniques generally involve a searchby means of some form of data manipulation-for a component of optical variability that is harmonically related to the radio pulsation. Although the general method has found spectacular success in the case of NP 0532 (Cocke, Disney, and Taylor 1969), it requires a reasonably accurate position for the radio pulsar for, otherwise, the photometer field aperture must be so large that the admitted sky light interferes to an undesirable extent with the sensitivity of the system to the sought-after signal. Thus, for a pulsar having only a poorly known position, direct photography may offer some advantages owing to the fact that the photographic plate is a panoramic device with the result that the interference contributed by the sky is limited approximately to the flux in a solid angle subtended by the actual recorded star image. To see that this is true, consider the photographic limiting magnitude for the Kitt Peak National Observatory 84-inch telescope

Double-beam vibrating mirror flying spot scanning-integrating microspectrophotometer.

Serial measurements of integrated ultraviolet absorbance of individual living cultured animal cells are possible with a double-beam scanning microscope designed to maximize the signal-to-noise ratio obtained for a given radiation flux traversing the sensitive specimen. A 192-line raster (2 sec/frame), scanned in the specimen plane by a focused spot of monochromatized radiation, is reconstructed by video technique to provide an image display and permit manual delineation of photometric fields of arbitrary shape, corresponding to the shape of the specimen. Analog circuits produce a read-out proportional to the integrated absorbance present in the photometric field, unaffected by inhomogeneity in the distribution of absorbing material.

Positive Afterimage as a Background Luminance*

In one experimental session, each of six subjects received six flashes of 1.4-msec duration from a centrally fixated 10° field of 4 × 105 L. The brightness of the afterimage was tracked, following the first two flashes, by means of a monocular bipartite photometric field. The bipartite field was formed by blocking one-half of the flash field to provide a semicircular afterimage and arranging a semicircular comparison field in juxtaposition. The comparison field could be varied over an 8-log-unit range by the subject. The density of the wedges was continuously recorded as the match was maintained. Recovery times for recognition of 28.7′ and 16.3′ Sloan Snellen letters at various luminance levels were measured following the other flashes. The letters were transilluminated and viewed against a dark surround. They were presented at one-second intervals and were at 140 mL immediately following the flashes. As soon as the subject correctly identified two successive letters, the luminance was reduced by introducing a neutral density filter. In this manner, ten luminance levels were measured following each flash, with the lowest 0.007 mL. The letters were superimposed on a 10° variable-luminance field and each subject determined the field luminance necessary for threshold recognition of each letter condition. The recovery times for the various letter conditions were then predicted for each subject from his afterimage brightness measurements and cross correlated with the measured recovery times. The correlation coefficient for the measured and predicted values was 0.82.

Positive afterimage following brief high-intensity flashes.

The time course of the decay of the positive afterimage following high-intensity flashes was measured by monocular and binocular brightness matching. The comparison field luminance was adjusted by means of crossed neutral wedges driven by a reversible motor. Density of the wedges was continuously recorded and the afterimage was tracked up to seven minutes following the flashes. Flash durations of 0.24 to 1.4 msec were used with a flash luminance of 4×105 L. With a 10° monocular bipartite photometric field, the afterimage brightness 5 sec following a 3×107 td·sec flash was matched by a 105-td comparison field. Photometric matches made monocularly or binocularly with an annular afterimage, 10° o.d. and 5° i.d., concentric with a 2° centrally fixated comparison field required approximately 104 td. A 2° central afterimage matched with an annular comparison field showed no significant difference from the annular afterimage. The results for the first two minutes following the flashes for all conditions showed a linear relationship between the logarithm of the comparison field luminance and the logarithm of the time measured from the flash.

A new use of the van Rhijn formula for airglow measurements

The formula of van Rhijn, relating the observed airglow intensity at any zenith angle to the zenith airglow intensity and emission altitude, is shown to be valid for observations made from above an airglow layer as well as below it. It is shown that it is sufficiently accurate to neglect the effects of finite photometer field of view, and of finite thickness of the emitting layer, with the limits on these parameters encountered in practice. An orthogonal set of photometers may be used to determine vehicle attitude, or to map out airglow irregularities using an unstabilized satellite.