{'fraction_non_alphanumeric': 0.026928422515635857, 'fraction_numerical': 0.01250868658790827, 'mean_word_length': 4.728358208955224, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
DEVELOPMENT OF A CLOUD PROFILINGFM-CW RADAR AT 94GHz

A cloud profiling radar transmitting frequency-modulated continuous wave (FM-CW) at 94GHz is developed for ground-based observations. Millimeter wave at 94GHz is used to realize high sensitivity to small cloud particles. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith. The radar is designed to observe clouds between 0.3 and 15 km in height with a resolution of 15 m. The system was integrated and sensitivities and stabilities have been measured. Results of test measurements of clouds will be presented. INTRODUCTION Comprehension of global environment and global change of climate is recently getting more and more important for the human beings in order to solve severe problems such as the greenhouse warming, the drying, the ozone holes and so on. It is necessary to know balance of solar energy coming to the Earth and cycle of water for the comprehension. One of the most significant features to know them is cloud, which reflects and absorbs incoming solar radiation, traps the radiation from the ground, transfers the energy in it, and radiates it outside. Information on 3-dimensional structures of clouds, sizes and distribution of cloud particles, dependence on size of optical characteristics of cloud particles, motions of particles in clouds, and so on are all desirable to solve role of clouds. Characteristics of clouds described above, however, have not been well known yet because of lack of enough observational data to present confidential results. Observations of clouds with radars would be most powerful method to derive the information because of following advantages: a) radio waves do not suffer from heavy extinction such as visible light, and consequently can investigate interior of clouds, b) the radar technique, which is an active sensing method, has great advantage of investigating interior structures of clouds to passive methods such as total power observations of irradiance of clouds, c) Doppler measurements of clouds which have low velocities around 10 m/sec is applicable only to radio frequency waves. Conventional radars operated at 5GHz can detect precipitation particles but are not able to detect particles in clouds because their sizes, less than a few tens microns, are much smaller that the wavelengths and, therefore, their cross sections are quite small. The cross sections of particles increase rapidly with frequency in Rayleigh scattering region. Rader observations of cloud particles at millimeter waves, which have been realized recently, have much more sensitive [1]. Several groups have reported the development and preliminary observational results that demonstrate powerful performances to investigate cloud particles [2],[3],[4]. We have designed and developed a cloud profiling radar at 94GHz. The purposes of the development of the FM-CW radar are a) evaluation and verification of an FM-CW radar at 94 GHz in Japan comparing to a pulse radar, b) obtaining millimeter wave FM-CW radar techniques and algorism of data reduction, and c) contribution to scientific research on cloud physics. In this paper, we present design concepts and specifications of the radar as well as results of test measurements of sensitivities, stabilities, and clouds. DESIGNE AND CONSTRUCTION Whole view of the developed radar is shown in Fig.1 [5]. FM-CW Radar We adopt a frequency-modulated continuous wave (FM-CW) radar rather than a pulse radar because the former can achieve more sensitive system than the latter if comparing with same instantaneous output power of transmitted millimeter wave. The principle of an FM-CW radar is shown in Fig.2. The signal frequency is modulated in the range of f0 F. Transmitted signal from one of the antennas is reflected by cloud particles, returns, and is received by the other antenna with a delay time of t relative to the original transmitted signal. Mixing the transmitted and received frequencies, beat frequencies fb are observed in the spectra, which are caused by ensemble of clouds particles: fb = 4 F r / (c Tm) (1), where r is the height of the clouds, Tm is the modulation interval, and c is the light velocity. When the objects move in the line of sight, the frequencies of reflected signals change by fd : fd = -2 ( f0 / c ) ( dr / dt ) (2). Fig.1. The developed cloud profiling FM-CW radar at 94GHz. Design Concept and Requirement Because one of the purposes of the facility is evaluation and verification of an FM-CW radar at 94 GHz, we design it to be a simple system so as to develop with commercially available components and to make maintenance and upgrade by ourselves. We designed the facility to observe clouds between 0.3 and 15 km in height with a resolution of 15 m. The velocities measured as Doppler shift should be less than 10 m/sec. The facility should be mobile for measurement in variety of places. Table 1. Designed parameters of antennas. Antenna Diameter 1 m f/D ration of Antenna 0.35 Antenna Optics Cassegrain Gain of Antennas 57 dBi Beam Width 0.18 degree Antenna Separation 1.4 m Direction of Antennas Zenith Polarization 1 Linear Antennas and Mounting According with the requirements described above, we decided parameters of antenna listed in Table 1 [6]. Transmitter and Receiver Section The block diagram of the transmitter and receiver section is shown in Fig.3 and parameters are summarized in Fig. 2. All signals including the transmitted FM-CW signal at 94GHz and local frequencies are generated from and/or ref rred to two signal generators in 140 MHz range, which are synchronized each other. e Fig.2. Principle of an FM-CW radar. Time Frequency