The computation of ocean wave heights from GEOS-3 satellite radar altimeter data

The GEOS-3 satellite, carrying a short pulse radar altimeter, was launched into orbit round the earth in April 1975. The altimeter was designed to provide an accurate measurement of the distance of the satellite above the earth, and also to record the shape of the radar return pulse as a measure of the mean roughness of the earth's surface. The satellite is intended to operate over the oceans, where surface height changes show variations in the earth's gravitational field, and roughness changes are due to waves.This paper is concerned with methods of determining waveheights from the shape of the radar return pulse and the corrections that have to be taken into account. The effects of timing variations on the shape of the average return pulse shape are discussed in detail. Accurate calibration of the sampling gates that measure this shape is found to be particularly critical.The waveheights deduced are compared with ground truth derived from ship reports on waveheights in the N.E. Pacific Ocean and routine measurements made at Ocean Weather Station PAPA. It is found that with suitable calibration and adjustments, the satellite measurements agree with surface observations to about 0.5 meters in $\text{H}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$.     

Remote sensing of leaf water content in the near infrared

A stochastic leaf radiation model was used to predict leaf spectral reflectance as a function of leaf water content for a dicot leaf. Simulated spectral reflectances were analyzed to quantify reflectance differences between different equivalent water thicknesses. Simulated results coupled with consideration of atmoshperic transmission properties and the incident solar spectral irradiance at the earth's surface resulted in the conclusion that the 1.55–1.75 μm region was the best-suited wavelength interval for satellite—platform remote sensing of plant canopy water status in the 0.7–2.5 μm region of the spectrum.     

Hierarchical channel router

The channel routing problem is a special case of the wire routing problem when interconnections have to be performed within a rectangular strip having no obstructions between terminals located on opposite sides of the rectangle.We present here a new channel routing algorithm, based on reduction of the problem to the case of a ($\text{2 × n}$) grid and on consistent utilization of a ‘divide-and-conquer’ approach. For the current implementation of the algorithm, the running time is proportional to $\text{N}{}^1\text{n}\text{log}\text{(m)}$ where $\text{N}$ is the number of nets, $\text{n}$ the length of the channel (number of columns) and $\text{m}$ the width of the channel (number of tracks).Traditional technological restrictions are assumed, ie, net terminals are located on vertical grid lines, two wiring layers are available for interconnections. One layer is used exclusively for vertical segments and another for horizontal. Vias are introduced for each layer change.This algorithm consistently outperforms several known routers in quality of wiring. We tested the algorithm on several benchmark problems. One of them, Deutsch's ‘difficult example’, was routed with only 19 horizontal wiring tracks (the absolute minimum for this case), whereas all other known routers required 20 or more tracks.     

Results of spectrophotometric measurements of natural formations from the spacecraft “Soyuz-9” and investigations of environment from space

During the “Soyuz-9” flight, the reflection spectra of various natural formations have been obtained by means of the handheld spectrograph RSS-2. Making use of the literature data on the surface reflection spectra for sand and water, the parameters of the atmospheric transfer operator were computed. The spectra obtained from the high altitude observations was corrected to spectral reflectance values at the earth's surface and compared with the curves for spectral radiance coefficients of different types of natural formations according to E. L. Krinov's classification. Using the parameters of the atmospheric transfer operator, the curves for spectral radiance coefficients of different types of natural formations as expected from space observations (Krinov's classification) have been computed.     

An integral equation method for inversion of electromagnetic soundings

The analogy of the problem of electromagnetic induction sounding of the earth's conductivity-depth profile using a two perpendicular-loop system to the general remote sensing problem of the atmosphere is pointed out. The induction sounding problem has been reduced to the solution of a new integral equation of Fredholm type. Kernels of the integral equation are evaluated, and their characteristics are investigated. A nonlinear relaxation inversion technique is suggested for the solution. Convergence of the solution, information content of measurements, and the range of possible retrieval of the conductivity profile are discussed.     

A steepest descents method for reentry optimization

A steepest descents optimization program is applied to the problem of a lifting vehicle entering the earth's atmosphere. The program employs penalty functions representing terminal conditions and inflight inequality constraints. During each iteration, it reduces a single performance measure which is the sum of the performance index and the penalty functions. Therefore, only one set of adjoint equations must be integrated per iteration.Values of weight factors, multiplying the penalty functions, are automatically adjusted before each iteration in order that the penalty functions will approach acceptable values. This method is shown to be a form of the classical Lagrange multiplier methods.     

Fibre-optic military communications

A high voltage surge, possibly as great as 25 kV/m, would be the pulse resulting from an exoatmospheric nuclear explosion at, say, 100–300 km above the earth's surface. In this case, it would do no physical harm to people or equipment, but within the few billionths of a second that the pulse lasts, it could disable a large part of vital military communications systems over an area as large as Western Europe. It is this split-second rise time of the electromagnetic pulse that makes conventional copper links so vulnerable, unless they have been previously ‘hardened’ or protected against the effects of surge currents. Accordingly, more emphasis is being placed on installing EMP-proff fibre-optic systems with individually screened electronic units or complete screened rooms, in which all sensitive system components are housed. The great advantages of optical cabling and light transmission were recognised for military security systems some years ago and now commerce and industry are benefiting from the military experience.     

Transmission of roll and pitch seat vibration to the head

A series of experiments has investigated the transmission of roll and pitch seat vibration to the heads of seated subjects. Head motion was measured in all six axes using a light-weight bite-bar while seated subjects were exposed to random motion at frequencies of up to 5 Hz at 1.0 rad.s ^?2 r.m.s. Subjects sat on a rigid flat seat in two body postures: ‘back-on’ (back in contact with backrest) and ‘back-off’ (no backrest contact). The influence of the position of the centre of rotation was also investigated.

Motion at the head occurred mostly in the lateral, roll and yaw axes during exposure to roll seat vibration and in the fore-and-aft, vertical and pitch axes during exposure to pitch seat vibration. A reduction in the magnitude of head motion occurred when the subjects sat in a 'back-off' posture compared with a 'back-on' posture. Varying the position of the centre of rotation along the lateral axis during roll seat vibration affected vertical and pitch head motion: least head motion occurred when the centre of rotation was in line with the subject's mid-sagittal plane. Varying the position of the centre of rotation along the vertical axis during roll seat vibration affected head motion in the mid-coronal plane: roll head motion decreased as the position of the centre of rotation was raised from below the seat surface to above the seat surface. Varying the centre of rotation (along the fore-and-aft and vertical axes) during pitch seat vibration altered head motion in the mid-sagittal plane. Head motion increased with increasing distance of the centre of rotation in front or behind the subject's ischial tuberosities and increased as the seat was raised from below the centre of rotation to above the centre of rotation.     

Radiative effects of elevated aerosol layer in Central Himalayas

Systematic observations of light detection and ranging (LIDAR) to detect elevated aerosol layer were carried out at Manora Peak (29.4° N, 79.5° E, ～1960 m a.s.l), Nainital, in the Central Himalayas during January–May 2008. In spite of being a remote, high-altitude site, an elevated aerosol layer is observed quite frequently in the altitude range of 2460–4460 m a.s.l with a width of ～2 km during the observation period. We compare these profiles with the vertical profiles observed over Gadanki (13.5° N, 79.2° E, ～370 m a.s.l), a tropical station, where no such elevated aerosol layer was found. Further, there is a steady increase in aerosol optical depth (AOD) from January (winter) to May (summer) from 0.043 to 0.742, respectively, at Manora Peak, indicating aerosol loading in the atmosphere. Our observations show north-westerly winds indicating the convective lifting of aerosols from far-off regions followed by horizontal long-range transport. The presence of strongly absorbing and scattering aerosols in the elevated layer resulted in a relatively large diurnal mean aerosol surface radiative forcing efficiency (forcing per unit optical depth) of about??65 and??63 W m^?2 and the corresponding mean reduction in the observed net solar flux at the surface (cooling effect) is as high as??22 and??30 W m^?2. The reduction of radiation will heat the lower atmosphere by redistributing the radiation with heating rate of 1.13 and 1.31 K day^?1 for April and May 2008, respectively, in the lower atmosphere.     

A theory of wave scatter from an inhomogeneous medium with a slightly rough boundary and its application to sea ice

An analytical theory of electromagnetic wave scattering from an inhomogeneous medium with a slightly rough boundary surface is formulated. The inhomogeneity in the medium is assumed to vary continuously in the vertical direction. In addition, it is also assumed to have a small random variation in the horizontal direction. The medium is assumed to consist of two layers. Maxwell's equations are solved by using the small perturbation method together with Fourier transform technique. The resulting differential equations are solved by using WKB and variation of parameter methods. Field amplitudes in each medium are determined by taking boundary conditions into account. The expressions for first order polarized radar backscatter cross-section δ⁰ are obtained. An attempt is made to apply the developed theory to compute sea ice scatter. The complex permittivity of sea ice, which depends on both the temperature and salinity, varies with the depth of sea ice. In addition, there is certainly some variation in the horizontal direction. Thus, the developed model may be able to give useful estimates when applied to sea ice scattering. Numerical calculations are performed for polarized radar backscatter cross-section ($\text{σ}{}_{\mathrm{<mtext>vv</mtext>}}{}^{\mathrm{<mtext>0</mtext>}}\text{and}\text{σ}{}_{\mathrm{<mtext>HH</mtext>}}{}^{\mathrm{<mtext>O</mtext>}}$) at two frequencies, 13.3 GHz and 400 MHz. It can be shown that WKB method is applicable at both of these frequencies. These theoretical results are compared with the experimental results obtained from NASA Earth Resources Program mission 126. Theoretical results give the same absolute value of σ^O and the relative variation among the six ice types as is given by the experimental results.     

Scratch drive actuator with mechanical links for self-assembly ofthree-dimensional MEMS

The self-assembling of three-dimensional (3-D) MEMS from polysilicon surface micromachined part is very attractive. To avoid risky external manipulation, the practical use of integrated actuator to perform the assembling task is required. To that goal, this paper presents detailed characteristics of the electrostatic surface micromachined scratch drive actuator (SDA). First, from numerous SDA tests, it is shown that this actuator is able to produce a threshold force of 30 μN, with a yield above 60%. With polysilicon devices consisting of SDA mechanically linked to buckling beam, a horizontal force of 63 mN has been demonstrated with ±112 V pulse, and up to 100 μN can be obtained with higher voltage. With buckling beams, displacements up to 150 μm have been obtained in the vertical direction. The generation of vertical force of 10 μN was confirmed with a 100 μm displacement producing 1 nJ work in the vertical direction. Finally, SDA overcomes the usual sticking of surface machined polysilicon by producing enough vertical force to completely release wide polysilicon plate (500 μm×50 μm) without external manipulation. The above characteristic, both in terms of structure releasing and vertical/horizontal forces and displacements provides the SDA with the capability of self-assembling complex 3-D polysilicon part, opening new integration capabilities and new application field of MEMS     

Limnological studies and remote sensing of the Upper Truckee River sediment plume in Lake Tahoe,California-Nevada

Five studies of the Upper Truckee River sediment plume in Lake Tahoe were conducted in California-Nevada using aerial photography and simultaneous measurements in the lake. The aerial and “water truth” studies covered a range of river discharge conditions during the snowmelt-runoff period in the spring of 1971. Color and multispectral aerial photography allowed delineation of the extent and relative density of four to five units within each plume. Simple correlation coefficients are high between these units and measures of suspended sediment, dissolved inorganic carbon, and light penetration, as well as measures of primary productivity and heterotrophic activity. Correlations are inconsistent between the above variables and nutrients (N-NO₃, P-PO₄, and Fe) apparently due to biological utilization of the latter in Tahoe's nutrient-poor environment. Two studies were conducted in the morning and afternoon of a single day; the plume's eastward shift during the day was recorded photographically and with limnological measurements. High correlations between sediment plumes and biological productivity coupled with evidence that silt particles and associated nutrients stimulate bacterial growth indicate that sediment plumes are accelerating the eutrophication of Lake Tahoe.     

The equivalence problem for two dpda's,one of which is a finite-turn or one-counter machine

For some non-real-time subclasses $\text{C}$ of deterministic pushdown automata (dpda), we give a general scheme to extend a decision procedure of the equivalence to that for two dpda's, one of which is in $\text{C}$. Using this scheme, we prove that the equivalence problem is decidable for two dpda's, one of which is a finite-turn or one-counter machine.     

An asymptotically optimal layout for the shuffle—exchange graph

The shuffle—exchange graph is one of the best structures known for parallel computation. Among other things, a shuffle-exchange computer can be used to compute discrete Fourier transforms, multiply matrices, evaluate polynomials. perform permutations, and sort lists. The algorithms needed for these operations are quite simple and many require no more than logarithmic time and constant space per processor. An $\text{O(}\text{N}{}^2\text{log}{}^2\text{N)-}\text{area}$ layout for the shuffle—exchange graph on a two-dimensional grid is described. The layout is the first which is known to achieve Thompson's asymptotic lower bound.     

An improved kernel function computation in subsonic unsteady lifting surface theory

A new and efficient scheme is presented for evaluating the kernel function K, which occurs in the linearized theory of oscillatory airloads on a planar lifting surface in subsonic flow. Among many previous efforts of this sort, the present paper was inspired by Ueda's method [10] for computing the integral function B(X, r, k) appearing in the kernel.Firstly we point out that important are not only B but also the remaining part A of the kernel, since singularities are latent in A as well as B. Moreover, it is quite desirable to express the singularities, which often must be treated analytically, by using the original variable x₀ rather than the modified one X.The second important problem concerns with the finite continuous part $\text{K}\text{?}{}^{\mathrm{F}}$, which must be numerically evaluated efficiently. A new method for this purpose is presented.This paper is restricted to the case where the frequency is real, namely the oscillation is neutrally stable.     

Reduction to the magnetic pole using a fast fourier series algorithm

An algorithm is developed for making magnetic field “reduction-to-the-pole” computations using two-dimensional Fourier series. A significant saving in computer time is achieved by using a “look-up table” to reduce the number of trigonometric functions to be evaluated. The algorithm is incorporated into an efficient FORTRAN program, RPØLE, for processing magnetic anomalies caused solely by induction in the earth's field.     

Lagrangian simulation of oil droplets transport due to regular waves

Dispersed oils (i.e., oil droplets) at sea are transported by convection due to waves and buoyancy and by turbulent diffusion. This work follows the common approach in the oil community of using a Lagrangian approach instead of the Eulerian approach. Our focus was on small scale simulation of oil plumes subjected to regular waves. Stokes' theory was used to obtain analytical expressions for wave kinematics. The velocity above the Mean Water Level was obtained using a second order Taylor's expansion of the velocity at the MWL. Five hundred droplets were used to simulate the plume for a duration of 60 wave periods. A Monte Carlo framework (300 simulations) was used to compute theoretical mean and variance of plumes. In addition, we introduced a novel dimensionless formulation, whose main advantage was to allow one to report distances in terms of the wave length and times in terms of the wave period. We found that the Stokes' drift was the major mechanism for horizontal transport. We also found that lighter oils propagate faster but spread less than heavier oils. Increasing turbulent diffusion caused the plume to disperse deeper in the water column and to propagate less forward. The spreading in both vertical and horizontal directions increased with an increase in turbulent diffusion. The increase in wave slope (or wave steepness) caused, in general, an increase in the downward and horizontal transport. In the context of mixing in the water column, the dimensionless formulation showed that small steepness waves with a large turbulent diffusion coefficient could result in essentially the same spreading as large steepness waves with a small turbulent diffusion coefficient.     

The graphical simulation of tectonic plate motion

LANDROT is a computer program written for the Natural Environment Research Council Honeywell 66/60 Computer to simulate landmass paleomovement by the rotation of geographic outlines about poles of rotation on the Earth's surface. The output is a plot using the NERC GRAFIX subroutine library with optional projections.     

Kupradze's functional equation for the torsion problem of prismatic bars — Part 1

St. Venant's torsion problem for a prismatic bar is reduced to an integral equation of the Fredholm type with the help of Kupradze's method: i.e. for a given load distribution on the lateral surface of the cylinder (“actual body $\text{K}{}^{\mathrm{+}}$”) imbedded in an elastic medium (“basic body $\text{K}{}^0$”), a distribution of screw dislocations has to be determined on the lateral surface in such a manner that the external region of the infinite medium (“complementary body $\text{K}{}^{\mathrm{?}}$”) will be free of tension. The unknown function is the tangential derivative of the warping function. Part 1 demonstrates the method for a smooth boundary. In part 2 the influence of the corners on the convergence of the numerical solution of the integral equation is investigated. Prismatic bars with multiconnected cross sections as well as cross sections with corners can be treated with this method.     

Variability and mechanisms of vertical distribution of aerosols over the Indian region

The present study investigates the seasonal variability in the vertical distribution of aerosol over the Indian region and its surroundings, and the possible mechanisms in the atmosphere that give rise to vertical transport of the aerosols. During boreal summer months, the aerosols reach a higher altitude of above 5 km over the Indian region. In the winter season, especially during December, January, and February, the aerosols remain at low levels of the atmosphere, extending to about 3 km. The low-level atmospheric conditions are favourable for lifting of aerosols associated with the organized convection in the atmosphere during the months from May to September. The shifting of the Inter Tropical Convergence Zone (ITCZ) towards the northern hemisphere and the monsoon activity associated with it makes the atmosphere turbulent over the region during the period. The vorticity and convergence patterns are favourable for the vertical transport of aerosols during the period from May to November. High vertical wind shear, which leads to the generation of turbulence during the monsoon season, enhances the mixing of aerosols in the atmosphere and supports the lifting motion. Over the Arabian Sea, during the summer months, the aerosols reach a higher altitude of about 6 km. The production of marine aerosols is increased by the monsoon winds over the sea, and the turbulent atmosphere lifts the particles to high altitudes. The transportation of dust aerosols from west and northwest parts is found at high altitudes towards the destination regions in north and south India. This also dominates the total aerosol content over the region.