An introduction to heat transfer

Underwater wireless information transfer is of great interest to the military, industry, and the scientific community, as it plays an important role in tactical surveillance, pollution monitoring, oil control and maintenance, offshore explorations, climate change monitoring, and oceanography research. In order to facilitate all these activities, there is an increase in the number of unmanned vehicles or devices deployed underwater, which require high bandwidth and high capacity for information transfer underwater. Although tremendous progress has been made in the field of acoustic communication underwater, however, it is limited by bandwidth. All this has led to the proliferation of underwater optical wireless communication (UOWC), as it provides higher data rates than the traditional acoustic communication systems with significantly lower power consumption and simpler computational complexities for short-range wireless links. UOWC has many potential applications ranging from deep oceans to coastal waters. However, the biggest challenge for underwater wireless communication originates from the fundamental characteristics of ocean or sea water; addressing these challenges requires a thorough understanding of complex physio-chemical biological systems. In this paper, the main focus is to understand the feasibility and the reliability of high data rate underwater optical links due to various propagation phenomena that impact the performance of the system. This paper provides an exhaustive overview of recent advances in UOWC. Channel characterization, modulation schemes, coding techniques, and various sources of noise which are specific to UOWC are discussed. This paper not only provides exhaustive research in underwater optical communication but also aims to provide the development of new ideas that would help in the growth of future underwater communication. A hybrid approach to an acousto-optic communication system is presented that complements the existing acoustic system, resulting in high data rates, low latency, and an energy-efficient system.

Underwater Optical Wireless Communication

[1] A newly discovered 1000-km scale longitudinal variation in ionospheric densities is an unexpected and heretofore unexplained phenomenon. Here we show that ionospheric densities vary with the strength of nonmigrating, diurnal atmospheric tides that are, in turn, driven mainly by weather in the tropics. A strong connection between tropospheric and ionospheric conditions is unexpected, as these upward propagating tides are damped far below the peak in ionospheric density. The observations can be explained by consideration of the dynamo interaction of the tides with the lower ionosphere (E-layer) in daytime. The influence of persistent tropical rainstorms is therefore an important new consideration for space weather. Citation: Immel, T. J., E. Sagawa, S. L. England, S. B. Henderson, M. E. Hagan, S. B. Mende, H. U. Frey, C. M. Swenson, and L. J. Paxton (2006), Control of equatorial ionospheric morphology by atmospheric tides, Geophys. Res. Lett., 33, L15108, doi:10.1029/2006GL026161. [2] The ionosphere is the region of highest plasma density in Earth’s space environment. It is a dynamic environment supporting a host of plasma instability processes, with important implications for global communications and geo-location applications. Produced by the ionization of the neutral atmosphere by solar x-ray and UV radiation, the uppermost ionospheric layer has the highest plasma density with a peak around 350–400 km altitude and primarily consists of O + ions. This is called the F-layer and it is considered to be a collisionless environment such that the charged particles interact only weakly with the neutral atmosphere, lingering long after sunset. The E-layer is composed of molecular ions and is located between 100–150 km where collisions between ions and neutrals are much more frequent, with the result that the layer recombines and is reduced in density a hundredfold soon after sunset [Rees ,1 989;Heelis, 2004]. The respective altitude regimes of these two layers are commonly called the E- and F-regions. [3] The ionosphere glows as O + ions recombine to an excited state of atomic oxygen (O I) at a rate proportional to

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006GL026161

Control of equatorial ionospheric morphology by atmospheric tides

The International Reference Ionosphere (IRI) project was established jointly by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) in the late sixties with the goal to develop an international standard for the specification of plasma parameters in the Earth’s ionosphere. COSPAR needed such a specification for the evaluation of environmental effects on spacecraft and experiments in space, and URSI for radiowave propagation studies and applications. At the request of COSPAR and URSI, IRI was developed as a data-based model to avoid the uncertainty of theory-based models which are only as good as the evolving theoretical understanding. Being based on most of the available and reliable observations of the ionospheric plasma from the ground and from space, IRI describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 km to 2000 km. A working group of about 50 international ionospheric experts is in charge of developing and improving the IRI model. Over time as new data became available and new modeling techniques emerged, steadily improved editions of the IRI model have been published. This paper gives a brief history of the IRI project and describes the latest version of the model, IRI-2012. It also briefly discusses efforts to develop a real-time IRI model. The IRI homepage is at http://IRImodel.org.

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The International Reference Ionosphere 2012 – a model of international collaboration

The international reference ionosphere (IRI) is the internationally recognized and recommended standard for the specification of plasma parameters in Earth’s ionosphere. It describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 to 1,500 km. A joint working group of the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) is in charge of developing and improving the IRI model. As requested by COSPAR and URSI, IRI is an empirical model being based on most of the available and reliable data sources for the ionospheric plasma. The paper describes the latest version of the model and reviews efforts towards future improvements, including the development of new global models for the F2 peak density and height, and a new approach to describe the electron density in the topside and plasmasphere. Our emphasis will be on the electron density because it is the IRI parameter most relevant to geodetic techniques and studies. Annual IRI meetings are the main venue for the discussion of IRI activities, future improvements, and additions to the model. A new special IRI task force activity is focusing on the development of a real-time IRI (RT-IRI) by combining data assimilation techniques with the IRI model. A first RT-IRI task force meeting was held in 2009 in Colorado Springs. We will review the outcome of this meeting and the plans for the future. The IRI homepage is at http://www.IRI.gsfc.nasa.gov.

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The international reference ionosphere today and in the future

The Floating Potential Measurement Unit (FPMU) is a multi-probe package designed to measure the floating potential of the 1nternational Space Station (ISS) as well as the density and temperature of the local ionospheric plasma environment. The role oj the FPMU is to provide direct measurements of ISS spacecraft charging as continuing construction leads to dramatic changes in ISS size and configuration. FPMU data are used for refinement and validation of the ISS spacecraft charging models used to evaluate the severity and frequency of occurrence of ISS charging hazards. The FPMU data and the models are also used to evaluate the effectiveness of proposed hazard controls. The FPMU consists of four probes: a floating potential probe, two Langmuir probes. and a plasma impedance probe. These probes measure the floating potential of the ISS, plasma density, and electron temperature. Redundant measurements using different probes support data validation by inter-probe comparisons. The FPMU was installed by ISS crewmembers, during an ExtraVehicular Activity, on the starboard (Sl) truss of the ISS in early August 2006, when the ISS incorporated only one 160V US photovoltaic (PV) array module. The first data campaign began a few hours after installation and continued for over five days. Additional data campaigns were completed in 2007 after a second 160V US PV array module was added to the ISS. This paper discusses the general performance characteristics of the FPMU as integrated on ISS, the functional performance of each probe, the charging behavior of the ISS before and after the addition of a second 160V US PV array module, and initial results from model comparisons.

https://ntrs.nasa.gov/api/citations/20070032723/downloads/20070032723.pdf

Initial Results from the Floating Potential Measurement Unit aboard the International Space Station

The Auroral Spatial Structures Probe (ASSP) is a NASA sounding rocket mission to be launched in the late January 2015 time frame that will be used to study both the spatial and temporal small scale variation of the electric and magnetic fields during active aurora and just before the onset of an auroral sub-storm. This will be accomplished through the use of a constellation of small payloads that separate relative to each other throughout a sounding rocket flight.

Auroral Spatial Structures Probe (ASSP)

The scientific community and NASA are continually evaluating and setting the direction of future Aeronomy missions, including those targeted at space weather Missions, and the required supporting technologies, have historically been outlined within strategic plans developed for NASA by the science community Many of the proposed future missions will require constellations that act as single missions, making coordinated observations as a single virtual instrument The science return occurs from the multi-point or spatially distributed observations and not from a collocation of a complex suite of instruments, as does the current model The only conceivable way many of these missions can be achieved is through the use of small, low-cost satellites Thus, future science objectives will very likely push the development of small satellites for constellation missions Within this paper we show the trend of Aeronomy science missions towards multiple spacecraft and outline some of the missions proposed by the science community requiring small satellites

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The Role of Small Satellites in Aeronomy

Integrated Solar-Panel Antenna Array for CubeSats (ISAAC) is a high gain, efficient, lightweight, conformal Xband antenna array that is integrated with solar panels of a CubeSat. The antenna design is modular and independent from the solar cells, and therefore allows off-the-shelf components. In addition, the antenna elements are of low profile and do not require significant surface real estate. ISAAC will suit a multi-unit (≥ 3U) CubeSat that has sufficient area for solar cells (hence the antennas), or a CubeSat with deployed panels. The paper examines three best antenna candidates: loop, cross dipole, and meshed patch. It is found that while all three can provide sufficient phase range for the reflectarray, loop geometry has the best tradeoff between optical transparency and the antenna gain. The paper also presents the element performance for different array periodicity lengths (lattice distance) such as half wavelength and sub-wavelength. The optimal ISAAC design promises more than 94% optical transparency and higher than 22 dB gain. The targeted application of ISAAC is for Near Earth Network (NEN), however, the design can be conveniently scaled to Space Network (SN) and Deep Space Network (DSN) radios.

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Integrated Solar-Panel Antenna Array for CubeSats (ISAAC)

Sweeping frequency plasma impedance probes have been flown on recent sounding rocket missions and also on the International Space Station. These plasma impedance probes have been used to 1) Characterize the low latitude ionosphere. 2) Study the descending layers in the E-region. 3) Measure the electron temperature, density, and electron-neutral collision frequency within mid-latitude spread F and 4) Measure the ambient plasma properties around the international Space Station. The impedance of the electrically short monopole, dipole or patch antenna used in these missions is determined by generating sweeps of radio frequency voltages between 200 kHz and 20 MHz as the spacecraft travels through the ionospheric layers and measuring the current at the probe input terminals. The impedance data is analyzed using a Plasma Fluid Finite Difference Time Domain (PF-FDTD) model developed at the Utah State University. In this study, the results of the PF-FDTD simulations are compared with the measured data obtained from the Sudden Atomic Layer (SAL) mission, which was launched as a part of the COQUI II campaign from Puerto Rico on 19th February, 1998 at 2009 LT. The parameters that were to be determined were the electron plasma frequency, electron gyro frequency and the ambient magnetic field in the altitude range of 90 – 115 Kms.

Charles Swenson

Papers

Initial Results from the Floating Potential Measurement Unit aboard the International Space Station

Auroral Spatial Structures Probe (ASSP)

The Role of Small Satellites in Aeronomy

Integrated Solar-Panel Antenna Array for CubeSats (ISAAC)

Plasma impedance probe analysis with a finite difference time domain simulation