manohar deshpande - Academia.edu (original) (raw)

Papers by manohar deshpande

Frontiers in Astronomy and Space Sciences

There continue to be open questions regarding the solar wind and coronal mass ejections (CMEs). F... more There continue to be open questions regarding the solar wind and coronal mass ejections (CMEs). For example: how do magnetic fields within CMEs and corotating/stream interaction regions (CIRs/SIRs) evolve in the inner heliosphere? What is the radially distributed magnetic profile of shock-driving CMEs? What is the internal magnetic structure of CMEs that cause magnetic storms? It is clear that these questions involve the magnetic configurations of solar wind and transient interplanetary plasma structures, for which we have limited knowledge. In order to better understand the origin of the magnetic field variability in steady-state structures and transient events, it is necessary to probe the magnetic field in Earth-directed structures/disturbances. This is the goal of the Multiview Observatory for Solar Terrestrial Science (MOST) mission (Gopalswamy et al., 2022). For MOST to answer the aforementioned questions, we propose the instrument concept of the Faraday Effect Tracker of Coro...

2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2017

A coherent bistatic vegetation scattering model, based on a Monte Carlo simulation, is being deve... more A coherent bistatic vegetation scattering model, based on a Monte Carlo simulation, is being developed to simulate polarimetric bi-static reflectometry at VHF/UHF-bands (240-270 MHz). The model is aimed to assess the value of geostationary satellite signals of opportunity to enable estimation of the Earth's biomass and root-zone soil moisture. An expression for bistatic scattering from a vegetation canopy is derived for the practical case of a ground-based/low altitude platforms with passive receivers overlooking vegetation. Using analytical wave theory in conjunction with distorted Born approximation (DBA), the transmit and receive antennas effects (i.e., polarization, orientation, height, etc.) are explicitly accounted for. Both the coherency nature of the model (joint phase and amplitude information) and the explicit account of system parameters (antenna, altitude, polarization, etc) enable one to perform various beamforming techniques to evaluate realistic deployment configurations. In this paper, several test scenarios will be presented and the results will be evaluated for feasibility for future biomass and root-zone soil moisture application using geostationary communication satellite signals of opportunity at low frequencies.

2016 Progress in Electromagnetic Research Symposium (PIERS), Aug 1, 2016

The main goal of this research is to design, fabricate, and test deployable VHF antennas for 6U C... more The main goal of this research is to design, fabricate, and test deployable VHF antennas for 6U Cubesat platforms to enable validation of root zone soil moisture (RZSM) estimation algorithms for signal of opportunity (SoOp) remote sensing over the 240-270 MHz frequency band. The

Gateway to the New Millennium. 18th Digital Avionics Systems Conference. Proceedings (Cat. No.99CH37033)

ABSTRACT A numerical method is presented to determine the electromagnetic shielding effectiveness... more ABSTRACT A numerical method is presented to determine the electromagnetic shielding effectiveness of a rectangular box with perforated walls. Expressing electromagnetic (EM) fields in terms of cavity Green's function inside the box and free space Green's function outside the box, integral equations with aperture tangential electric fields as unknown variables are obtained by enforcing the continuity of tangential magnetic field across the apertures. Using the Method of Moments (MoM), the integral equations are solved for unknown aperture fields. From a knowledge of the aperture fields, the EM field inside a rectangular box with perforated walls due to external EM sources are determined. Numerical data of EM shielding effectiveness of a rectangular box with a single aperture and multiple apertures is presented and validated with experimental and earlier published data

This software innovation is designed to develop a mathematical formulation to estimate the electr... more This software innovation is designed to develop a mathematical formulation to estimate the electromagnetic scattering characteristics of complex, inhomogeneous objects using the finite-element-method (FEM) and method-of-moments (MoM) concepts, as well as to develop a FORTRAN code called FEMOM3DS (Finite Element Method and Method of Moments for 3-Dimensional Scattering), which will implement the steps that are described in the mathematical formulation. Very complex objects can be easily modeled, and the operator of the code is not required to know the details of electromagnetic theory to study electromagnetic scattering.

Advanced Digital Beamforming (DBF) Synthetic Aperture Radar (SAR) technology is an area of resear... more Advanced Digital Beamforming (DBF) Synthetic Aperture Radar (SAR) technology is an area of research and development pursued at the NASA Goddard Space Flight Center (GSFC). Advanced SAR architectures enhances radar performance and opens a new set of capabilities in radar remote sensing. DBSAR-2 and EcoSAR are two state-of-the-art radar systems recently developed and tested. These new instruments employ multiple input-multiple output (MIMO) architectures characterized by multi-mode operation, software defined waveform generation, digital beamforming, and configurable radar parameters. The instruments have been developed to support several disciplines in Earth and Planetary sciences. This paper describes the radars advanced features and report on the latest SAR processing and calibration efforts. Keywords—component; Digital Beamforming, interferometry SAR, InSAR.

Space borne microwave remote sensors at VHF/UHF frequencies are important instruments to observe ... more Space borne microwave remote sensors at VHF/UHF frequencies are important instruments to observe reflective properties of land surfaces through thick and heavy forestation on a global scale. One of the most cost effective ways of measuring land reflectivity at VHF/UHF frequencies is to use signals transmitted by existing communication satellites (operating at VHF/UHF band) as a signal of opportunity (SoOp) signal and passive receivers integrated with airborne/space borne platforms operating in the Low Earth Orbit (LEO). One of the critical components of the passive receiver is two antennas (one to receive only direct signal and other to receive only reflected signal) which need to have ideally high (>30dB) isolation. However, because of small size of host platforms and broad beam width of dipole antennas, achieving adequate isolation between two channels is a challenging problem and need to be solved for successful implementation of space borne SoOp technology for remote sensing....

IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36194)

The scattering properties of arbitrarily shaped microstrip patch antennas are examined. The elect... more The scattering properties of arbitrarily shaped microstrip patch antennas are examined. The electric field integral equation for a current element on a grounded dielectric slab is developed for a rectangular geometry based on Galerkin's technique with subdomain rooftop basis functions. A shape function is introduced that allows a rectangular grid approximation to the arbitrarily shaped patch. The incident field on

19th DASC. 19th Digital Avionics Systems Conference. Proceedings (Cat. No.00CH37126)

ABSTRACT An analytical method is presented to estimate EM energy coupled to a wire residing in th... more ABSTRACT An analytical method is presented to estimate EM energy coupled to a wire residing in the fuselage of an aircraft. A fuselage with a wire inside is modeled by a metallic rectangular cavity with a wiring inside and rectangular windows on its side walls. Using the equivalence principles and the rectangular cavity Green's functions, the EM fields inside the cavity due to the equivalent current sources on windows and wires are determined. By matching the tangential magnetic fields across the apertures and equating the total tangential electric field over the cylindrical surface of wires to zero, coupled integro-differential equations are obtained. The integro-differential equations in conjunction with the Method of Moments (MoM) are then solved for the unknown magnetic and electric current amplitudes. One of the advantages of the present approach is that it gives an accurate and efficient analytical model for the EM coupling studies which is computationally less intensive compared to other numerical methods. Numerical data on EM energy coupled to a cylindrical wire of various lengths and oriented along the two principle axes of rectangular cavity is presented. From the numerical data it is concluded that a cylindrical wire of length nλ/4 where n is an odd integer, would pick up maximum energy

Root zone soil moisture (RZSM) is not directly measured by any current satellite instrument, desp... more Root zone soil moisture (RZSM) is not directly measured by any current satellite instrument, despite its importance as a key link between surface hydrology and deeper processes. Presently, model assimilation of surface measurements or indirect estimates using other methods must be used to estimate this value. Signals of Opportunity (SoOp) methods, exploiting reflected P- and S-band communication satellite signals, have many of the benefits of both active and passive microwave remote sensing. Reutilization of active transmitters, with forward-scattering geometry, presents a strong reflected signal even at orbital altitudes. Microwave radiometry is advantageous as it measures emissivity, which is directly related to dielectric constant and sensitive to water content of soil. Synthetic aperture radar (SAR) is used in P-band (400 MHz) for soil moisture and biomass, but faces issues in obtaining permission to transmit due to spectrum regulations, particularly over North America and Europ...

A precise knowledge of the interior structure of asteroids, comets, and Near Earth Objects (NEO) ... more A precise knowledge of the interior structure of asteroids, comets, and Near Earth Objects (NEO) is important to assess the consequences of their impacts with the Earth and develop efficient mitigation strategies. Knowledge of their interior structure also provides opportunities for extraction of raw materials for future space activities. Low frequency radio sounding is often proposed for investigating interior structures of asteroids and NEOs. For designing and optimizing radio sounding instrument it is advantageous to have an accurate and efficient numerical simulation model of radio reflection and transmission through large size bodies of asteroid shapes. In this presentation we will present electromagnetic (EM) scattering analysis of electrically large size asteroids using (1) a weak fonn fonnulation and (2) also a more accurate hybrid finite element method/method of moments (FEM/MOM) to help estimate their internal structures. Assuming the internal structure with known electric...

Design and Development of VHF Antennas for Space Borne Signal of Opportunity Receivers for Cubesa... more Design and Development of VHF Antennas for Space Borne Signal of Opportunity Receivers for Cubesat Platforms. Space borne microwave remote sensors at VHF/UHF frequencies are important instruments to observe reflective properties of land surfaces through thick and heavy forestation on a global scale. One of the most cost effective ways of measuring land reflectivity at VHF/UHF frequencies is to use signals transmitted by existing communication satellites (operating at VHF/UHF band) as a signal of opportunity (SoOp) signal and passive receivers integrated with airborne/space borne platforms operating in the Low Earth Orbit (LEO). One of the critical components of the passive receiver is two antennas (one to receive only direct signal and other to receive only reflected signal) which need to have ideally high (>30dB) isolation. However, because of small size of host platforms and broad beam width of dipole antennas, achieving adequate isolation between two channels is a challenging ...

Bi-static reflection measurements utilizing global navigation satellite service (GNSS) or other s... more Bi-static reflection measurements utilizing global navigation satellite service (GNSS) or other signals of opportunity (SoOp) can be used to sense ocean and terrestrial surface properties. End-to-end calibration of GNSS-R has been performed using well-characterized reflection surface (e.g., water), direct path antenna, and receiver gain characterization. We propose an augmented approach using on-board receiver electronics for radiometric calibration of SoOp reflectometers utilizing direct and reflected signal receiving antennas. The method calibrates receiver and correlator gains and offsets utilizing a reference switch and common noise source. On-board electronic calibration sources, such as reference switches, noise diodes and loop-back circuits, have shown great utility in stabilizing total power and correlation microwave radiometer and scatterometer receiver electronics in L-band spaceborne instruments. Application to SoOp instruments is likely to bring several benefits. For exa...

IEEE Transactions on Antennas and Propagation

A method is presented to determine the active input impedance of an infinite array of rectangular... more A method is presented to determine the active input impedance of an infinite array of rectangular patches embedded in a dielectric layer. The reaction integral equation is used to include details of feed structure into the formulation. The matching performance over wide scan angles of the printed antenna with a dielectric cover is studied. The results obtained by the present

EcoSAR is an advanced airborne polarimetric and "single pass" interferometric P-band (4... more EcoSAR is an advanced airborne polarimetric and "single pass" interferometric P-band (435 MHz) SAR instrument developed at NASA/Goddard Space Flight Center. The instrument was designed to provide two- and three-dimensional fine scale measurements of terrestrial ecosystem structure and biomass, relevant to the study of the carbon cycle and its relationship to climate change. EcoSAR fisrt test flights and science campaign took place in late March 2014 aboard a NOAA P3 aircraft, conducting measurements over areas of the Bahamas and Costa Rica.

2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)

2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Jul 1, 2016

In this investigation, we aim to collect and use time-series multi-frequency microwave data over ... more In this investigation, we aim to collect and use time-series multi-frequency microwave data over winter wheat during entire growth cycle to characterize vegetation dynamics and to quantify its effects on soil moisture retrievals. We plan to incorporate C-band radar and VHF receiver within the existing L-band radar/radiometer system called ComRAD (SMAP's ground based simulator). With C-band's ability to sense vegetation details and VHF's root-zone soil moisture within ComRAD's footprint, we will be able to test our 'discrete scatterer' vegetation models and parameters at various surface conditions. The purpose of this study is to determine optical depth and effective scattering albedo of vegetation of a given type (i.e. winter wheat) at various stages of growth that are need to refine soil moisture retrieval algorithms being developed for the SMAP mission.

1981 Antennas and Propagation Society International Symposium