In the classical development of wind profiler systems, the VHF range (40-60 MHz) has been generally selected for high altitudes explorations (ST and MST systems) and the UHF range oriented mainly towards low altitudes soundings (T systems). Preliminary experiments in LSEET have shown that it was possible to investigate as low as 300 m with a low-power, small 50 MHz profiler radar in a classical configuration (squared, nxn). Bur using a small antenna array involves an increasing of the half-power beamwidth and of the overlapping in adjacent gates in oblique directions, and inverse methods have to be applied for atmospheric parameters retrieval. A new configuration of the antenna (two crossed lines) leads to decrease the oblique angle and the half-power beamwidth, and allows to reduce overlapping between adjacent gates. In this paper, measurements from the small profiler in these two different configurations (squared and crossed configurations) and from the Provence radar (reference radar) will be: compared, without using inverse methods. Validities of small radar measurements for horizontal velocities will be given in a quantitative way, as a function of the altitude and of the signal-to-noise ratio. Conclusions will be clearly exposed, and will indicate that measurements from the small profiler in crossed configuration ape not strongly affected by overlapping, and that then horizontal velocities can be interpreted directly without using inverse methods.

A new technique of full decoding of truncated ranges applicable to complementary codes is presented. For code length of N, the technique uses a set of N/2 complementary code pairs to obtain a diagonal decoding matrix M that enables the full decoding of truncated ranges without the need of matrix inversion, and resulting in optimum performance with regards to the signal-to-noise ratio degradation (SNRD) in the truncated ranges. Techniques of constructing the required code sequences for code length of 4, 8, 16, 32, etc., are given. By arranging the order of transmission of the code sequences systematically to increase the suppression of sidelobes resulting from atmospheric characteristics, and by performing appropriate steps to reduce the effects of interferences, it is shown that a coding system that simultaneously optimizes the performances with regards to SNRD, sidelobe suppression, and interference rejection can be obtained. Examples are given to illustrate this.

An approach based on matrix formulation used for the representation and analysis of the signals and processes in ST/MST radar systems using a series of polyphase code sequences is presented. Expressions of the appropriate signals at various stages of the transmitting/receiving and processing channels of the system are given, using mostly matrix formulation, which has the advantage, among other things, of compactness. The expressions of the powers of the various components of the received signal, including the geophysical signal and interference signals, are obtained in order to derive expressions for performance parameters such as those related to the degradation of signal-to-noise ratio in the truncated ranges and interference suppression. Analysis tools for obtaining optimum solutions to the full decoding of truncated ranges, interference suppression, and reduction of sidelobes resulting from atmospheric characteristics are developed.

Under ideal conditions, complementary code pairs produce no sidelobes. In practice, sidelobes are produced, among other things, when the period of the Doppler frequency shift as well as the time of coherence of clear air turbulence are comparable (or smaller) than the interpulse period. The intensity of sidelobes increases with the radar operating frequency and becomes a real problem in the upper VHF and UHF bands. In this paper, a new technique for reducing sidelobes originating from atmospheric characteristics for clear air radar systems using pulse coding is presented. For this, a generalized analytic expression for a sidelobe suppression factor applicable to any number of binary code sequences is first derived. This is then used to develop the technique, which in the case of complementary codes consists of manipulating the order of transmission of the code sequences. For such codes, improvements in sidelobe suppression of the order of 80 dB on the VHF frequency band are obtained. The modifications required to implement the technique into existing systems are very few and simple.