Jayesh P. Pabari

Radio Frequency Modelling for Future Wireless Sensor Network on Surface of the Moon

In order to study lunar regolith properties, wireless sensor network is planned to be deployed on surface of the Moon. This network can be deployed having few wireless sensor nodes capable of measuring soil properties and communicating results, as and when ready. Communication scenario on lunar surface is quite different as compared to that on the Earth, as there is no atmosphere and also there are lots of craters as well as various terrain topologies. Since the deployment of sensors on the Moon is a challenging and difficult task, it is advisable to predict the behaviour of communication channel on lunar surface. However, communication models like Irregular Terrain Model used for terrestrial communication networks are not directly applicable for Unattended Ground Sensor type sensor networks and need modifications according to lunar surface conditions and lunar environment. Efforts have been put to devise a model of radio frequency environment on the Moon using basic equations governing various physical phenomena occurring during radio propagation. The model uses Digital Elevation Model of four sites of the Moon, measured by Terrain Mapping Camera on board Chandrayan-1, a recent Indian mission to the Moon. Results presented in this paper can provide understanding of percentage area coverage for given minimum received signal strength, potential sites for sensor deployment assuring wireless communication, decision whether a given sensor node can work and can provide suggestion for possible path of rover with cluster head to remain in contact with the nodes. Digital Elevation Model based results presented here can provide more insight in to the communication scenario on the Moon and can be very useful to mission planners.

Development of Impedance-Based Miniaturized Wireless Water Ice Sensor for Future Planetary Applications

Keeping in view the future in situ space applications, to study planetary surface science, we have designed and developed an impedance-based extremely compact wireless sensor node to infer the presence of water/ice in a soil sample and reported in this paper. Although reflectometry-based soil moisture sensors are available commercially, they have slightly longer probe, needing more volume, from the payload point of view. The reported wireless impedance sensor reproduced in space-qualified form can be useful to measure the permittivity of lunar regolith and infer the presence of water ice. It works in the frequency domain with capability to sweep the frequency in a given measurement range. The sensor does not necessarily have long probe, and it needs only electrical contact with the soil surface, thus eliminating extra energy for insertion by the rover on the lunar surface, in one of its possible space applications. The sensor has been made to operate in wireless mode, which is a basic need in any space applications. The data are transmitted at 2.4 GHz to the aggregator. We have tested sand-type terrestrial soil and lunar soil simulant JSC-1A. To verify the performance of the sensor, we have also tested Milli-Q water. All these experimental results are reported in this paper. Results of Milli-Q water, whose permittivity is known, agree with those reported in the literature, verifying excellent performance of the sensor. Thus, the sensor can be very useful for space applications, where size and weight are critical issues. A wireless impedance sensor can also be quite useful for terrestrial applications, for example, in agriculture, and also in other impedance-based applications.

Efficient extension of conventional low frequency filter bank spectrometer by implementation of high resolution Chirp Z signal processing

The spectral analysis of any signal involves a signal-processing tool using Fourier processors. Chirp Z Transform (CZT) is a modern technique providing ideally any frequency resolution in the spectrum. The conventional filter bank type spectrometer provides low to moderate (few 100 kHz) frequency resolution and if its frequency resolution is to be increased further then the number of channels must be increased to a large extent, necessitating extra hardware and expense. To increase the frequency resolution of a conventional filter bank further, a novel approach using Chirp Z transform has been suggested at low frequency. It is a cost effective and easy to use solution capable of providing both Chirp Z signal processing and Discrete Fourier Transform (DFT) as a special case of CZT. It is an efficient way to perform offline signal processing in applications not requiring real time operation.

Investigations on groove design for modulating frequency response of SAW RAC chirp filter

Surface Acoustic Wave (SAW) Reflective Array Compressor (RAC) type chirp filters are used in radar compressive receivers as matched filters or compressors. The conventional way of designing the grooves in such filters is to make groove length constant throughout the length of the array. However, this does not give levelled frequency response and shows a rise toward the high frequency side. A new idea of tapering the groove length is suggested in this article. The suggested design shows that the frequency response of the chirp filter is flat in the frequency range of interest compared with a conventional one. Simulated results are shown for a chirp filter with centre frequency 450 MHz and bandwidth of 200 MHz.

Design, Implementation and Testing of Signal Processing Module for an Impact Ionization Dust Detector

The study of dust at high altitudes on the Mars has been in literature for a long time and a few sources are expected, which can contribute to it. Recent MAVEN observations found the dust from about 150 to 1000 km height from the Mars surface and it is expected to be interplanetary in nature. An in situ measurement of dust at orbital altitude is needed to study the dust and a few attempts were made in past in this direction. An impact ionization dust detector, called Mars Orbit Dust Experiment (MODEX) has been proposed to find the source, abundance, flux and distribution of the dust at Mars by future orbiter. A prototype model of the dust detector is under development at PRL. The detector principle, its electronics design, implementation, simulation and testing are presented in this article. Also, back end processing and derivation of the signal parameters are included along with user interface for the analysis. The signal processing module could be useful for detection of a charge pulse generated due to dust impact.

Revisiting Lunar Water Ice Content Retrieval Using Lunar Remote Sensing Data

During a few recent lunar missions, a possibility of water ice existing in the permanently shadowed regions on the moon has come forward. The content of water ice on the moon is an open question in the current moon study. It is known that the existence of ice mixed with regolith can affect permittivity of the lunar surface material and consequently to the microwave brightness temperature of the lunar surface. In this paper, we have considered the measured permittivity of the lunar soil simulant JSC-1A and the pure ice. A few dielectric mixing models have been discussed and Odelevsky model has been used to derive the effective permittivity of the mixture. The microwave brightness temperature has been simulated using two layer lunar regolith model. The relationship between the microwave brightness temperature and the water ice content has been arrived at using the derived effective permittivity. The microwave brightness temperature of the lunar surface obtained by Change-1 has been used. From the study, it has been found that there is a possibility of upper regolith layer with about 9cm can have the volume water ice content of about 2.943%.

Receiver development for 300-3000 GHz region

Limitations imposed by the atmosphere at terahertz (THz) frequencies have restricted researchers from retrieving crucial information regarding astronomical sources. With the availability of sensitive detectors and new generation of telescopes, the terahertz instrumentation has improved drastically over the past two decades. High spectral resolution information retrieved from star forming molecular system is very essential in understanding the model of evolution process of stars and galaxies. In this paper, we will present the development of a submillimeter wave (300-3000 GHz) receiver system to study interstellar molecular clouds dynamics and chemistry.

High resolution chirp transform spectrometer

In the submillimeter (SMM) region of electro-magnetic spectrum, heterodyne techniques are widely used to achieve high spectral resolution. The SMM source signal and a known local oscillator signal are mixed in a nonlinear device in order to generate an intermediate frequency (IF), which retains the spectrum of SMM source. The IF1 thus obtained from first mixer stage is down converted to required frequency of 1250 MHz to make it suitable for further processing in spectrometer. To extract the spectral information of source signal various spectrometers are used. The chirp transform spectrometer (CTS) is the state-of-the-art spectrometer (Hartogh and Hartmann, 1990) to achieve very high frequency resolution. The key element of CTS is a surface acoustic wave (SAW) based chirp filter capable of providing desired frequency resolution. We present the details of system design of the spectrometer, digital generation of expander chirp signal and the reflective array compressor (RAC) type SAW chirp filter.