Quadrature Sampling with High Dynamic Range

Many radio and sonar systems require signal outputs in complex low-pass form. To achieve this, it is possible to use uniform sampling of the bandpass signal, together with computation of the quadrature component by way of a Hilbert transform. The bandpass to low-pass translation is accomplished by undersampling. A hardware implementation is described which achieves 70 dB spurious-free dynamic range and a bandwidth of 30 kHz.     

Design Rules for Adaptive Arrays

The concepts of "equivalent linear arrays" and "minimum effective spacing" can be used to simplify the analysis of planar adaptive arrays. The resulting design rules permit the rapid determination of array configurations without the need for computer modeling.     

Absolute IR-spectra from the measurement of Fourier-spectrometers aboard Meteor 25 and 28

It is well known that temperature- and watervapour-profiles, ozone concentration, other atmospheric constituents and the surface-radiation of the Earth can be determined by remote sensing in the IR radiation range with the aid of a satellite.

The narrow-band radiation measurements for remote sensing of the atmosphere and the Earth-surface can be realized either by various radiometers working in selected frequency channels or, continuously in a given frequency range, by spectrometers with fixed spectral resolution.

Fourier-spectrometers (FS) have been used in Earth-orbit only four times up to now: Nimbus 3, Nimbus 4, Meteor 25 and Meteor 28.

The most important technical parameters, the working regime and some aspects of date processing of the FSs working aboard of Meteor 25 and Meteor 28 are given. For the determination of calibrated absolute spectra a method is used that is based on the experience of the first experiment and on the long time stability of the spectrometers. The results obtained in laboratory calibration tests and in the orbit are described.     

Reliability of the Station-Keeping Activator Subsystem of a Geostationary Satellite

The reliability of the station-keeping activator subsystem of a geostationary satellite using electric thrusters is analyzed by modeling the probabilistic behavior of the system as a homogeneous Markov process. The method is applied to the particular case of a 400-kg satellite using 1.5-mN cesium contact electric thrusters. lt is shown that certain system configurations offer a mass improvement without loss of reliability.     

Non-intrusive methods for temperature measurements in liquid zones in microgravity environments

Material Science and Life Science experiments in microgravity both have urgent needs of evaluating the temperature distribution within and on the surface of liquid zones. Non intrusive methods are available which measure the IR radiations emitted by the surface. The thermograph systems have a number of advantages since they supply a thermal picture of the surface with sufficient time, space and temperature accuracy. A computerized system has been designed for data acquisition and elaboration and used for ground experiments; the system can also be used for space experiments with some modifications. Non intrusive measurements of bulk temperature in two dimensional liquid flow fields can be made by means of optical methods which detect variations of the index of refraction. A method is proposed which is able to take with the same optical apparatus shadowgraph. Schlieren and differential interferometers pictures. A computerized system is proposed for data acquisition and elaboration.     

Computerized Model Demonstrating Magnetic Submarine Localization

A modet is described which consists of an aircraft with flux gate magnetometers mounted on the wing tips and a submarine containing a magnet to simulate the induced and permanent fields of an actual submarine. Equations are developed which enable a minicomputer sampling the magnetometers to calculate the location, depth, and heading of the submarine as the aircraft travels towards it. The real time plotted results are presented.     

Modified Barker and Huffman Sequences in Combination Codes

lt is possible that usable combination codes can be obtained if Barker and Huffman sequences are chosen as the inner and outer codes. lt is shown that an improvement in either energy efficiency or time sidelobe structure will result either from a modification of a Huffman sequence or from a modification of a Barker sequence. Results are given for a combination code of length 91, with inner and outer codes of length 7 and 13.     

Device for mass measurement under zero-gravity conditions.

The problem considered in this paper is the investigation of the properties of a mass-meter, i.e. the device for determining the mass of cosmonaut's body under zero-gravity conditions. The estimates of accuracy of mass measurement by this device are given, and the results of measuring the masses of cosmonauts' bodies on the Salyut 5 and 6 orbital stations are presented.     

Comparison of ozone data derived from SBUV and SAGE with emphasis on longitudinal variations

Stratospheric ozone observations by the SAGE and SBUV satellite instruments in March and April, 1979 have been analyzed. All SAGE profiles have been smoothed vertically over 8 km to provide some compatibility with the SBUV vertical resolution. Comparing the zonal mean ozone mixing ratios against smoothed LIMS profiles, it is inferred that SAGE is systematically overestimating ozone by approximately 20% at tropical latitudes at pressures lower than 5 mb and that SBUV is underestimating ozone by approximately 15% at 50–70° latitude at 10 mb. A comparison of the longitudinal variations of ozone by SBUV and SAGE is made and the detectability of planetary waves in ozone is emphasized. The uncorrelated portion of the SAGE variances are found to be approximately consistent with the SAGE noise model. Based on the correlated variances, the amplitudes of the smoothed SAGE planetary waves in ozone are found to be the same, on average, as in the SBUV experiment at mid-latitudes between 1 and 10 mb. Planetary wave detectability is illustrated during two several day periods at mid-latitudes and a persistent and theoretically-consistent relationship between ozone and temperature is noted. These examples, however, indicate that differences between ozone planetary wave amplitudes derived from the two sensors may occur when there is a strong vertical gradient in wave amplitude.     

Small Aperture Angle Measurement for Active Echo Location Systems

The problem of bearing estimation for active systems is examined from the point of view of the generalized wideband ambiguity function (GAF). The maximum likelihood (ML) estimator is derived and its local and global properties are discussed. A structure is proposed which searches the three-dimensional ambiguity surface in two stages first, in range-Doppler, and then, in bearing with the goal of reducing search complexity when utilizing highly resolvent waveforms. Comparisons are made between the ML estimators and structures utilizing phase information which generate closed form estimators. The beneficial results of full bandwidth utilization are discussed in terms of both local and global properties of the GAF.