Mr. Prantik Chakraborty Profile

Prantik Chakraborty

at Space Applications Ctr

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Publications (4)

SPIE Journal Paper | 21 July 2023

Wideband digital multi-channel merge-split fast Fourier transform spectrometer: design and characterization

Shikha Sharma, Mahendra P. Singh, Prantik Chakraborty, Rajeev Jyoti

JATIS, Vol. 9, Issue 03, 034002, (July 2023) https://doi.org/10.1117/12.10.1117/1.JATIS.9.3.034002

KEYWORDS: Spectroscopy, Analog to digital converters, Field programmable gate arrays, Spectral resolution, Telescopes, Carbon monoxide, Receivers, Fourier transforms, Equipment, Galactic astronomy

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We developed a wideband multi-channel merge-split fast Fourier transform spectrometer (FFTS) using analog-to-digital convertors (ADC) for signal sampling and field-programmable gate arrays (FPGA) for real-time spectrum generation. The FFTS constitutes the backend of the sub-mm wave heterodyne spectroscopy telescope to observe emitted radiations from rotational transitions of CO (J: 2 → 1 and J: 3 → 2) with 50 arc sec angular resolution, aiming to provide the first comprehensive survey of molecular clouds in the Milky Way and nearby galaxies from the northern hemisphere (Hanle, India) at these frequencies. The FFTS provides 8 GHz instantaneous bandwidth at 1.6 MHz spectral resolution (extendable to 0.8 or 0.4 MHz) comprising four channels (spanning 218.898 to 220.898 GHz, 229.038 to 231.038 GHz, 329.087 to 331.087 GHz, and 344.295 to 346.295 GHz frequency bands) belonging to two receiver chains at 230 and 345 GHz operating in a double side band configuration. The channel placement for these four channels is done to cover 13CO (J:2 → 1) transition at 220.398 GHz, 12CO (J:2 → 1) transition at 230.538 GHz, 13CO (J:3 → 2) transition at 330.588 GHz, and 12CO (J:3 → 2) transition at 345.796 GHz with 1.5 GHz margin for red-shifts. Spectrometer design is presented along with spectral line profile simulations, hardware configuration, proposed methodology, system specifications, and scalable field-programmable gate arrays (FPGA) implementation architecture. Elements in the instrument design leverage simultaneous multi-channel acquisition for optimized FPGA utilization by merging the channel pair from the sideband separating (2SB) second stage intermediate frequency (IF) mixer during Fourier transform and subsequently splitting the generated spectra. System characterization results are presented, confirming instruments capable of stable spectroscopy with a wide bandwidth (instantaneous 8 GHz with four 2 GHz channels) and high-spectral sampling (1 / 0.5 / 0.25 MHz corresponding to scalable fast Fourier transform length of 4k / 8k / 16k respectively) that provides adequate spectral resolution for the science case. Wide dynamic range (49.3 dB) and fine radiometric resolution required for relative spectroscopic measurements is realized by sampling IF signals with 12-bits ADCs. Variable spectral accumulation time facilitates improvements in the signal to noise ratio proportional to the square root of the number of coherent averaged cycles, covering various target dependent (longer dwell time for a single target) or scanning dependent (e.g., drift scanning mode matching earth’s rotation) dwell time requirements.

Proceedings Article | 17 May 2016 Paper

A high-resolution scanning pencil-beam scatterometer: system design challenges

Prantik Chakraborty, Priyanka Gupta, Tapan Misra

Proceedings Volume 9878, 98780R (2016) https://doi.org/10.1117/12.2228162

KEYWORDS: Ku band, Scatterometry, Synthetic aperture radar, Doppler effect, Antennas, Radar, Electroluminescence, Spatial resolution, Space operations, Satellites

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The scanning pencil-beam Scatterometer configuration is pretty effective in covering a large ground-swath by rotating a moderately sized paraboloid dish at a moderate speed. For example, Oscat (Oceansat-II Scatterometer) did cover a ground-swath of 1550km using a 1m diameter reflector that was rotated at 20.5 rpm. The decade-long service (1999-2009) provided by the Seawinds instrument onboard the Quikscat mission followed by an almost half-a-decade (2009-2014) service of Oscat has made this configuration tremendously popular with the global user community. A major drawback of conventional pencil-beam systems like Seawinds and Oscat is the relatively poor spatial resolution. The ground-resolution is beamwidth-limited azimuthally while, in elevation, the resolution is improved by engaging pulse-compression and range-binning. Oscat’s Instantaneous Field of View (IFOV) was 25km wide in azimuth (az) and 50km in elevation (el) at 49° incidence angle. The range-compressed resolution bins had dimensions of 6km (el) x 25km (az). Therefore, qualified wind products could be generated upon square grids no finer than 25km x 25km resolution. According to recommendations of International Ocean Vector Wind Science Team (IOVWST) and Oscat user community, high-resolution scatterometry is the requirement of the day with wind-vector cell-size dimension of 5km or better. One way to improve the resolution is to adopt the SAR principle of Range-Doppler discrimination in the scanning pencil-beam configuration. The footprint can be resolved simultaneously in range as well as in azimuth, thus significantly improving the size of the combined Range-Doppler resolution bin (~ 1km). However, the addition of Doppler filtering to conically scanning radar brings with it its own disadvantages e.g. the limitations of dwell time and the constant change in orientation of isodop lines. This paper presents the constraints in system design of high-resolution scanning systems, the design trade-offs, the methods of handling high PRF, the radar pulsing scheme and the achievable resolution.

Proceedings Article | 5 May 2016 Paper

A novel atmospheric Temperature Sounding Unit: system design and performance analyses

Prantik Chakraborty, Priyanka Gupta, Dilip Dave, Nilesh Desai, Tapan Misra

Proceedings Volume 9876, 98761H (2016) https://doi.org/10.1117/12.2228155

KEYWORDS: Radiometry, Oxygen, Signal attenuation, Sensors, Antennas, Atmospheric modeling, Absorption, Calibration, Reflectors, Polarization

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Proceedings Article | 8 December 2006 Paper

Spatial resolution enhancement and interpolation using Backus-Gilbert inversion: demonstration with TMI brightness temperature data

Prantik Chakraborty, Arundhati Misra

Proceedings Volume 6410, 64100P (2006) https://doi.org/10.1117/12.692882

KEYWORDS: Antennas, Resolution enhancement technologies, Image enhancement, Temperature metrology, Spatial resolution, Sensors, Image processing, Microwave radiation, Super resolution, Image resolution

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