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2022 | Buch

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Satellite Measurements of Clouds and Precipitation

Theoretical Basis

verfasst von: Hirohiko Masunaga

Verlag: Springer Nature Singapore

Buchreihe : Springer Remote Sensing/Photogrammetry

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This book provides a thorough introductory description of the physical principles underlying the satellite remote sensing of clouds and precipitation. A diverse collection of satellite sensors is covered, including imagers, radars, and sounders over a broad spectral range from visible to microwave radiation.
The progress in satellite instrument technology during the past two decades as represented by the Tropical Rainfall Measuring Mission (TRMM), CloudSat, and Global Measurement Mission (GPM) satellites has drastically improved our capability of measuring clouds and precipitation across the globe. At the same time, such rapid progress makes it increasingly challenging for scientists without specialized skills in remote sensing to fully grasp how satellite measurements are being made. This book is designed to mitigate that challenge. The targeted readers are graduate students and professional scientists seeking an extended summary of the theoretical background behind observations from space, ranging from fundamental physics (the statistical mechanics and radiative processes, for instance) to more practical levels of theory such as retrieval algorithm design.

Inhaltsverzeichnis

Frontmatter

General Background

Frontmatter

Chapter 1. Introduction

Abstract

This chapter offer a concise introduction to the following chapters. There are numerous satellite data products freely accessible that contain a variety of cloud and precipitation parameters. For a user new to satellite remote sensing, the challenge would be probably not the lack of choice but that there are too many options to choose from. The user is advised to be aware that the same variable could be derived from various types of sensors with uncertainties of different nature. Cloud amount from infrared radiance is not identical to lidar-based cloud amount, and precipitation from microwave brightness temperature never precisely agrees with radar-derived precipitation. Even the same parameter from the same kind of instruments may give diverse answers when the measurements are made from different orbits or processed through different retrieval algorithms. Expert knowledge is instrumental for disentangling all these complex issues involved in the construction of satellite data products. This book is hoped to be a little fountain of useful knowledge on the basic principles of satellite remote sensing.

Hirohiko Masunaga

Chapter 2. Satellite Missions and Instruments

Abstract

In this chapter, satellite missions targeted on cloud and precipitation measurements are first outlined, followed by an overview of instruments aboard. It is not intended to go through a complete catalog of missions and instruments ever sent into orbit, but is instead to focus on the present and relatively recent satellite programs at the time of this writing. The reader new to satellite remote sensing might be overwhelmed at first by an inundation of acronyms, but there is of course no need to memorize all these abbreviations. The names of missions are not of eternal value anyway in that all satellite programs will soon become outdated (or may have already so for future readers). Nevertheless, the heritage of key mission objectives and instrument capabilities at present time will be passed on to future satellite programs with the underlying basics remaining largely unchanged. The ultimate goal of this chapter is to illustrate such ageless fundamentals of satellite technologies.

Hirohiko Masunaga

Chapter 3. Satellite Orbit and Scan

Abstract

Choosing the optimal orbit is a critical step for designing satellite programs to meet given mission goals. Fundamentals of orbital mechanics, with emphasis on those relevant to meteorological satellites, are reviewed for illustrating the physical background behind different types of satellite orbits mentioned. While the geostationary orbit (GEO) stands on a very simple physical principle, the physics underlying low-earth orbits (LEOs), for which a higher-order spherically-asymmetric component of the earth’s gravity field (the \(J_2\) perturbation) is crucial, is far more complicated than GEO. This chapter provides a compact but complete derivation of the \(J_2\) perturbation formula along with its implications for LEO configurations. The second half of the chapter is devoted to an overview of the instrument design such as the field of view and scanning geometry.

Hirohiko Masunaga

Basic Physics

Frontmatter

Chapter 4. Principles of Statistical Mechanics

Abstract

The interactions between radiation and matter are essential for understanding the physical foundations of remote sensing. This chapter is devoted to a brief review of the statistical mechanical principles underlying the radiative processes. The interactions of thermal radiation with media, the Planck function for a notable example, are understood in terms of statistical mechanics. Another crucial theoretical element behind satellite remote sensing is the radiative transfer equation, which describes the propagation of photon energy over a distance by a simple transport equation known as the radiative transfer equation. In this chapter, the radiative transfer equation is derived in light of the Boltzmann equation of photons.

Hirohiko Masunaga

Chapter 5. Principles of Electrodynamics and Geometrical Optics

Abstract

In this chapter, a brief introduction to electrodynamics is first provided to review the theoretical basis how electromagnetic waves are modified in magnitude and direction as they propagate through different media. It is then demonstrated that Maxwell’s equations are of great utility for quantifying the radiative properties of particle scattering and absorption. The second half of the chapter is devoted to a short summary of geometrical optics. Geometrical optics, although a simple, empirical framework of ray tracing predating Maxwell’s theory, is also useful in satellite observations for characterizing the emission and reflection of radiation at the earth’s surface.

Hirohiko Masunaga

Chapter 6. General Theory of Radiative Processes

Abstract

This chapter focuses on the microscopic physical processes responsible for the emission and absorption of radiation. The opening section describes some basic properties of the Planck function and related physical principles, followed by detailed discussions of the theoretical background behind the atmospheric gas and condensate spectra. The microwave gas spectrum is constituted of a limited number of absorption lines owing to molecular oxygen and water vapor transitions, while the infrared gas spectrum is a full of absorption lines primarily from vibrational transitions of water vapor and carbon dioxide molecules. Water condensates give rise to their own spectral features distinct from the gaseous counterpart. The chapter offers an introductory course to outline the physical basis of those radiative properties of atmospheric constituents.

Hirohiko Masunaga

Measurement Principles

Frontmatter

Chapter 7. Infrared Sensing

Abstract

Thermal infrared radiation is a convenient tool for cloud remote sensing. Infrared emissions from cloud tops are often considered to be a proxy of the temperature there (and hence of cloud top height) regardless of day or night. Infrared brightness temperature, however, is not always a reasonable substitute for the physical temperature of clouds and could be largely misinterpreted if analyzed without care. The chapter begins with the theory of non-scattering radiative transfer, followed by simulated infrared spectra to demonstrate the impacts of clouds on satellite measurements. The ultimate goal of this chapter is to present the utility and limitations of the satellite infrared measurements of cloud properties such as cloud top temperature, particle size, and thermodynamic phase.

Hirohiko Masunaga

Chapter 8. Visible/Near-Infrared Imaging

Abstract

Satellite visible imagery is intuitive in interpretation because visible remote sensing is the way by which human eyes observe the surrounding world. Our eyes are an optical device with a set of overlapping spectral filters that help us make sense out of the world through “colors”. RGB-composite satellite images visualize the entire earth that would be seen if we could fly out of the planet. Satellite visible/infrared imagers, however, are not designed just to mimic human vision. In the context of meteorological applications, the primary purposes include the quantitative evaluation of the cloud physical properties such as cloud optical depth and effective radius. This chapter is devoted to a review of the methodologies of visible/near-infrared cloud measurements from satellites with focus on their theoretical background. The chapter begins with the theory of scattering radiative transfer without thermal emission, followed by simulated infrared spectra to demonstrate the impacts of clouds on satellite measurements.

Hirohiko Masunaga

Chapter 9. Microwave Radiometry

Abstract

Microwave radiation of the terrestrial origin is weak in intensity compared to thermal infrared radiation since microwave frequencies are away from the blackbody spectral maximum corresponding to the earth’s surface temperature. The smallness of hydrometeors relative to wavelength acts to reduce the efficiency of absorption and scattering at microwave frequencies. By contrast, the dielectric function of liquid water increases drastically with wavelength from the infrared to microwave ranges, implying that cloud and rain water actively interacts with microwave radiation. These different properties competing against one another constitute the unique utility of microwave remote sensing. Microwave radiometry conveys useful information for measuring precipitation as well as cloud LWP and column water vapor. The physical principles behind the microwave observations of atmospheric constituents are discussed in this chapter.

Hirohiko Masunaga

Chapter 10. Active Remote Sensing

Abstract

In late 1997, the launch of the Tropical Rainfall Measuring Mission (TRMM) satellite marked the beginning of a new era of satellite remote sensing, adding (literally) a new dimension to cloud and precipitation observations from space. TRMM Precipitation Radar (PR) was the first spaceborne weather radar, having provided valuable observations of three-dimensional precipitating cloud structure during its 17-year operation until 2014. A second breakthrough was brought about by the CloudSat W-band radar and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar, which, although limited to nadir observations unlike PR, have enabled to profile the vertical structure of a broad spectrum of clouds from thin cirrus to deep convection towers. The TRMM PR was succeeded by its follow-on instrument Dual-frequency Precipitation Radar (DPR) aboard the Global Precipitation Measurement (GPM) core observatory with an improved capability to detect light and frozen precipitation. This chapter is dedicated to concise descriptions of the theoretical basis and algorithmic strategies behind radar and lidar observations.

Hirohiko Masunaga

Chapter 11. Mathematical Basis of Retrieval Algorithms

Abstract

We have seen in the preceding chapters the physical principles of satellite remote sensing in terms principally of the radiative transfer theory. Cloud properties impact on visible and infrared radiances, and precipitation modulates microwave brightness temperature. Satellite retrieval algorithms involve a “reverse engineering” of the radiative transfer theory so that the cloud and precipitation properties are traced back from radiance and brightness temperature. This chapter provides a brief overview of theoretical guidance for deciphering the satellite-received electromagnetic signals to identify and reconstruct the observed geophysical parameters.

Hirohiko Masunaga

Applications

Frontmatter

Chapter 12. Global Datasets of Clouds and Precipitation

Abstract

Satellite measurements play crucial roles in the construction of global observation datasets of clouds and precipitation. Many of such datasets are open to public, but there are so many choices it is hard to decide which one best suits your needs. This chapter is meant to be a concise guidance for those in need of a little assistance. It is not attempted in this chapter to present a complete list of satellite-based cloud/precipitation products, since otherwise the reader would be inundated with excessive information. Instead, we will put focus on a limited number of datasets that are widely used in the science and commercial/industrial sectors. Following an introduction to the data processing levels, selected data products are summarized without going too much into technical details.

Hirohiko Masunaga

Chapter 13. Satellite Data Simulators

Abstract

Satellite data simulators, a general term for a software package containing a set of atmospheric radiative transfer codes and a user interface, provide synthetic satellite measurements (observables such as radiance and/or retrieved variables) for geophysical variables input by users. In other words, a satellite data simulator generates virtual observations from hypothetical satellite instruments. This chapter offers a concise introduction to satellite data simulators with a selected list of simulator packages. The second section is devoted to detailed descriptions of model setups in the radiative transfer simulations carried out for this book.

Hirohiko Masunaga

Backmatter

Titel: Satellite Measurements of Clouds and Precipitation
verfasst von: Hirohiko Masunaga
Verlag: Springer Nature Singapore
Electronic ISBN: 978-981-19-2243-5
Print ISBN: 978-981-19-2242-8
DOI: https://doi.org/10.1007/978-981-19-2243-5