Refinement and Validation of a Real-time Airborne System for Remotely Sensing Ocean Surface using Communication Satellite Signals

The ability to remotely sense ocean wave heights and wind speed by measuring the reflected Radio Frequency (RF) signals from the ocean’s surface has been demonstrated in previous research projects. The recording systems for these research projects collected and stored unmodified RF signals and then analyzed the data through post-processing. Several disadvantages to this approach include large requirements for data storage and lengthy post-processing time. To assist in the creation of a suitable platform for an airplane-based application, a new system was designed which features real-time processing of the RF signals. This system captures two RF signals in the 2.4 GHz regions (direct and reflected), calculates the cross-correlation between the two signals and then outputs the result to a PC. Due to the time-consuming nature of the cross-correlation algorithm, a FPGA based implementation of the system was chosen to conform to the real-time constraints of the system. In this project, previously created Verilog source code for the system was debugged, improved and verified. This project also developed a method to test the system by using several 110-foot sections of RG6 Coaxial Cables. These cables induced a physical delay in the reflected channel, simulating the application’s conditions, in order to cause a shift in the correlation peak. The results are discussed as well as suggestions for future improvements

Remote sensing using I-Band and S-Band signals of opportunity

Measurement of soil moisture, especially the root zone soil moisture, is important in agriculture, meteorology, and hydrology. Root zone soil moisture is concerned with the first meter down the soil. Active and passive remote sensing methods used today utilizing L-band(1-2GHz) are physically limited to a sensing depth of about 5 cm or less. To remotely sense the soil moisture in the deeper parts of the soil, the frequency should be lowered. Lower frequencies cannot be used in active spaceborne instruments because of their need for larger antennas, radio frequency interference (RFI), and frequency spectrum allocations. Ground-based passive remote sensing using I-band(0.1-1GHz) signals of opportunity provides the required sensing depth and solves the problems that come with the spaceborne remote sensing instruments using I-band reflectometry. A dual monopole antenna setup was used with one on the ground for direct signal and one 30m above ground for the reflected signal. The reflectivity and therefore the soil moisture was obtained from the differences between direct and reflected signals. Initially, an S-band (2-3GHz) signal was used as a proof of concept and its ease of implementation because of its higher transmitted power and stationary satellite. This experiment provides conclusions about the root zone soil moisture based on our observation and comparison of direct and reflected satellite signals of two different frequency bands and determination of reflectivity

Using P-band Signals of Opportunity Radio Waves for Root Zone Soil Moisture Remote Sensing

Retrieval of Root Zone Soil Moisture (RZSM) is important for understanding the carbon cycle for use in climate change research as well as meteorology, hydrology, and precision agriculture studies. A current method of remote sensing, GNSS-R uses GPS signals to measure soil moisture content and vegetation biomass, but it is limited to 3-5 cm of soil penetration depth. Signals of Opportunity (SoOp) has emerged as an extension of GNSS-R remote sensing using communication signals. P-band communication signals (370 MHz) will be studied as an improved method of remote sensing of RZSM. P-band offers numerous advantages over GNSS-R, including stronger signal strength and deeper soil penetration. A SoOp instrument was installed on a mobile antenna tower in a farm field at Purdue University in West Lafayette, IN. An additional half-wave dipole antenna, as well as corresponding modifications to the experiment’s front-end box, was included to capture horizontally-polarized reflected P-band signals throughout a corn growth season. By measuring the reflected signal power off the soil over time, soil moisture and above-ground biomass can be measured. Soil moisture and vegetation biomass change the soil’s dielectric reflection coefficient and thus affect its reflectivity properties. It is expected that there will be strong correlation between reflected signal strength and soil moisture. Data will be compared against soil moisture measurements from in-situ soil sensors. The data obtained will be used to verify existing analytical soil moisture and above-ground biomass models. In addition, these results will be used to build an airborne and/or space-based remote sensing instrument

Fluid structure in the immediate vicinity of an equilibrium three-phase contact line and assessment of disjoining pressure models using density functional theory

We examine the nanoscale behavior of an equilibrium three-phase contact line in the presence of long-ranged intermolecular forces by employing a statistical mechanics of fluids approach, namely density functional theory (DFT) together with fundamental measure theory (FMT). This enables us to evaluate the predictive quality of effective Hamiltonian models in the vicinity of the contact line. In particular, we compare the results for mean field effective Hamiltonians with disjoining pressures defined through (I) the adsorption isotherm for a planar liquid film, and (II) the normal force balance at the contact line. We find that the height profile obtained using (I) shows good agreement with the adsorption film thickness of the DFT-FMT equilibrium density profile in terms of maximal curvature and the behavior at large film heights. In contrast, we observe that while the height profile obtained by using (II) satisfies basic sum rules, it shows little agreement with the adsorption film thickness of the DFT results. The results are verified for contact angles of 20, 40 and 60 degrees

Generalized dynamical density functional theory for classical fluids and the significance of inertia and hydrodynamic interactions

We study the dynamics of a colloidal fluid including inertia and hydrodynamic interactions, two effects which strongly influence the non-equilibrium properties of the system. We derive a general dynamical density functional theory (DDFT) which shows very good agreement with full Langevin dynamics. In suitable limits, we recover existing DDFTs and a Navier-Stokes-like equation with additional non-local terms.Comment: 5 pages, 4 figures, 4 supplementary movie files, I supplementary pd

Snooping Around: Observation Planning for the Signals of Opportunity P-Band Investigation (SNOOPI)

Launching October 2022, the SigNals Of Opportunity P-band Investigation (SNOOPI) is a 6U CubeSat dedicated to demonstrating spaceborne remote sensing of root zone soil moisture and snow water equivalent using signals of opportunity. P-band (240-500 MHz) frequencies are required to penetrate dense vegetation or snow and into the top 200 cm of soil, but this band is heavily subscribed. Rather than transmitting its own signal SNOOPI will observe reflected signals from the U.S. Navy’s Mobile User Objective System satellites. This makes planning observations challenging. The point of reflection is a function of both the transmitter and receiver satellite positions as well as terrain. The direct signal must be observed simultaneously on the same antenna pattern with sufficient gain. Ionospheric delay must also be accounted for. To satisfy these requirements and maintain a cadence of one observation per day, the SNOOPI science operations center at Purdue University has developed custom software for scheduling activities onboard the satellite. The software is highly automated, involving the user only in the definition of observation targets, priorities, and giving final approval to the proposed schedule. Orbit, attitude, power, communication, memory, and observation constraints are handled by a combination of linear programming and pattern search optimization methods. The purpose of this paper is to describe the challenges of scheduling observations for a signals of opportunity mission and illustrate how they were solved for SNOOPI

The Radio Frequency Environment at 240-270 MHz with Application to Signal-of-Opportunity Remote Sensing

Low frequency observations are desired for soil moisture and biomass remote sensing. Long wavelengths are needed to penetrate vegetation and Earths land surface. In addition to the technical challenges of developing Earth observing spaceflight instruments operating at low frequencies, the radio frequency spectrum allocated to remote sensing is limited. Signal-of-opportunity remote sensing offers the chance to use existing signals exploiting their allocated spectrum to make Earth science measurements. We have made observations of the radio frequency environment around 240-270 MHz and discuss properties of desired and undesired signals

Dynamical density functional theory for orientable colloids including inertia and hydrodynamic interactions

Over the last few decades, classical density-functional theory (DFT) and its dynamic extensions (DDFTs) have become powerful tools in the study of colloidal fluids. Recently, previous DDFTs for spherically-symmetric particles have been generalised to take into account both inertia and hydrodynamic interactions, two effects which strongly influence non-equilibrium properties. The present work further generalises this framework to systems of anisotropic particles. Starting from the Liouville equation and utilising Zwanzig's projection-operator techniques, we derive the kinetic equation for the Brownian particle distribution function, and by averaging over all but one particle, a DDFT equation is obtained. Whilst this equation has some similarities with DDFTs for spherically-symmetric colloids, it involves a translational-rotational coupling which affects the diffusivity of the (asymmetric) particles. We further show that, in the overdamped (high friction) limit, the DDFT is considerably simplified and is in agreement with a previous DDFT for colloids with arbitrary shape particles.Comment: dynamical density functional theory ; colloidal fluids ; arbitrary-shape particles ; orientable colloid

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Design of an Instrument for Soil Moisture and Above Ground Biomass Remote Sensing Using Signals of Opportunity

Measurements of soil moisture are a crucial component for understanding the global water and carbon cycle, weather forecasting, climate models, drought prediction, and agriculture production. Active and passive microwave radar instruments are currently in use for remote sensing of soil moisture. Signals of Opportunity (SoOp) based remote sensing has recently emerged as a complementary method for soil moisture remote sensing. SoOp reuses general digital communication signals allowing the reuse of allocated wireless communication signal bands for science measurements. This thesis developed a tower based SoOp instrument implementing frequencies in the P-Band and S-Band. Two field campaigns were conducted using this new instrument during the summers of 2017 and 2018 at Purdue’s Agronomy Center for Research and Education