Solar Energy at Urban Scale

Benoit Beckers, Benoit Beckers

• Publisher: Wiley-ISTE
• Year: 2013
• ISBN:
  9781118614365
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Power Resources
• Index: Technology & Engineering

Increasing urbanization throughout the world, the depletion of fossil fuels and concerns about global warming have transformed the city into a physical problem of prime importance. This book proposes a multi-disciplinary and systematic approach concerning specialities as different as meteorology, geography, architecture and urban engineering systems, all surrounding the essential problem of solar radiation.
It collects the points of view of 18 specialists from around the world on the interaction between solar energy and constructions, combining territorial, urban and architectural scales to better regulate energetic efficiency and light comfort for the sustainable city.
The main subjects covered are: measures and models of solar irradiance (satellite observations, territorial and urban ground measurements, sky models, satellite data and urban mock-up), radiative contribution to the urban climate (local heat balance, radiative-aerodynamics coupling, evapotranspiration, Urban Heat Island), light and heat modeling (climate-based daylight modeling, geometrical models of the city, solar radiation modeling for urban environments, thermal simulation methods and algorithms) and urban planning, with special considerations for solar potential, solar impact and daylight rights in the temperate, northern and tropical climates, and the requirement of urban solar regulation.

Contents

1. The Odyssey of Remote Sensing from Space: Half a Century of Satellites for Earth Observations, Théo Pirard.
2. Territorial and Urban Measurements, Marius Paulescu and Viorel Badescu.
3. Sky Luminance Models, Matej Kobav and Grega Bizjak.
4. Satellite Images Applied to Surface Solar Radiation Estimation, Bella Espinar and Philippe Blanc.
5. Worldwide Aspects of Solar Radiation Impact, Benoit Beckers.
6. Local Energy Balance, Pierre Kastendeuch.
7. Evapotranspiration, Marjorie Musy.
8. Multiscale Daylight Modeling for Urban Environments, John Mardaljevic and George Janes.
9. Geometrical Models of the City, Daniel G. Aliaga.
10. Radiative Simulation Methods, Pierre Beckers and Benoit Beckers.
11. Radiation Modeling Using the Finite Element Method, Tom van Eekelen.
12. Dense Cities in the Tropical Zone, Edward Ng.
13. Dense Cities in Temperate Climates: Solar and Daylight Rights, Guedi Capeluto.
14. Solar Potential and Solar Impact, Frédéric Monette and Benoit Beckers.
Appendix 1. Table of Europe's Platforms (Micro- and Minisatellites) for Earth Observations, Théo Pirard.
Appendix 2. Commercial Operators of Earth Observation (EO) Satellites (as of January 1, 2012), Théo Pirard.
Appendix 3. Earth's Annual Global Mean Energy Budget, Benoit Beckers.

Chapter 1

The Odyssey of Remote Sensing from Space: Half a Century of Satellites for Earth Observations ¹

The operational venture of remote sensing spacecraft started in 1960 following two separate paths: the civilian weather observatories using television (TV) cameras for low-resolution images as well as the military spy satellites with high-resolution photographic films returning to Earth in recoverable capsules. The community of meteorological forecasters was the first one to use the dimension of space to embrace atmospheric changes and weather conditions on a global scale. The intelligence services of the USA and the Soviet Union (now Russia) used powerful telescopes to take precise pictures revealing many details on the ground. The problem for the early remote sensing from space, using optical systems, was that cloud cover prevents the satellites from taking useful photographs much of the time.

As spy satellites were able to observe the military operations in an adversery’s camps, the world of the 1960s was saved from the catastrophic move of a “Cold War” between two nuclear powers of this time toward a severely “hot conflict” which would have impacted the survival of the whole planet! Half a century later, today’s world is saved from the environmental tragedy of global climate change, mainly due to the images (collected every hour) and continuous data, which are currently collected by Earth observation (EO) satellites. Space, along with processing systems, is our new dimension for control of the globe for environmental and security purposes. Among the priorities to develop space as an asset serving the citizens of the world, the European Union (EU) has, along with the civilian Galileo constellation for geo-positioning, deployed the Global Monitoring for Environment and Security (GMES) program. It consists of five different Sentinel families of operational spacecraft and sensors in orbit, all “made in Europe”.

1.1. To improve the weather forecasts

To see our planet from space has been a dream since the beginning of the space age. It is still the purpose of most of the student teams, which are currently developing low-cost CubeSats (1–2 kg) for technological education. The first remote sensing satellites, with low-resolution imaging capabilities, were dedicated to meteorological observations. Using TV-type cameras, they are able to monitor the evolution of the clouds reflecting the sunlight. The weather satellite system, designed and operated for the continuous imaging survey of the globe, was based on the Television Infrared Observation Satellite (TIROS), developed by the National Aeronautics and Space Administration (NASA). The spin-stabilized Tiros-1 satellite was launched on April 1, 1960, and was operational for only 78 days in the 700 km altitude range. It opened the way to permanent operations with more reliable and more sophisticated spacecraft for weather forecasts. Some of its essential features remain unchanged in its later versions used even today, by Russian, European, Chinese, Japanese, Indian, and Korean meteorological satellites.

Before the advent of satellites, weather bureaus collected data from weather stations, ships, buoys, and balloons disseminated around the globe. The satellites are more expensive than these ground systems, but they can collect more globally instantaneous information with innovative sensors (spectrometers, sounders, etc.) for a larger field of vision. The information thus collected has to be updated and enhanced by in situ observations. Nowadays, weather satellites show the parameter by which the weather on the far side of the world would affect our meteorological conditions in a span of 4 or 5 days’ time. Sequences of pictures from geosynchronous satellites — positioned on a circular orbit at approximately 35,800 km above the equator — show cloud formations in the Pacific Ocean traveling all the way across Canada before reaching Europe. With the amount of data collected by polar satellites regarding the atmospheric phenomena — in sun-synchronous orbit between 500 and 1,000 km of altitude — and their quick processing by powerful computers, it is possible to establish accurate weather forecasts for one week in advance.

The principle of remote sensing by optical satellites is to record with accurate precision the intensity of the Sun’s reflected light on the surface of the Earth. The number of pixels in the image taken by the camera dictates the graininess or resolution, namely the ability to blow it up and observe greater detail. The more pixels in an image, the more you can magnify it without making it grainy. On the other hand, the more pixels in a camera, the fewer the images you can store in the memory and consequently the more capacity you need to transmit it over the network for processing. The resolution hence obtained is on par with the swath: if the images have to capture some critical details, you will reduce the angle of view required to observe the desired areas. The camera fixed on the Tiros works on the principle of TV-type cathode-ray tube technology, with wide-angle capability. The images obtained show only a few details: the smallest features visible in weather images typically being 1 km in size. This lack of detail in the images obtained is a constraint due to the limited frequency bandwidth of the satellite to transmit such images to small ground receivers.

The US weather satellites, both in sun-synchronous and geosynchronous orbits, are owned and operated by the National Oceanic and Atmospheric Administration (NOAA) under the authority of the Department of the Interior. In parallel, the Department of Defense (DOD) had its own polar weather satellites within the Defense Meteorological Satellites Program. To reduce expenditure, an attempt was recently made to combine the weather programs of both the DOD and NOAA. However, the objective is still yet to be realized. In Europe, the first weather satellite Meteosat-1 was developed and operated in geosynchronous orbit by the European Space Agency (ESA). Once it became operational, the Meteosat system was transferred to the intergovernmental Eumetsat organization that owns and operates the satellites and the associated satellite control and data processing facilities. Other geosynchronous satellites for weather observations, indigenously manufactured, are used in Russia by Roskomgidromet, in Japan by the Japan Meteorological Agency (JMA), in India by the Indian Space Research Organization (ISRO), and in China by the China Meteorological Administration (CMA). The observations thus recorded are complemented by images and data obtained from polar spacecraft, also built by these countries.

1.2. Technological challenges to spy and to map from orbit

Satellites fly across the sky unhindered by borders, typically in the range of 200–800 km above ground level. In the mid-1950s, the American Central Intelligence Agency (CIA) used a fleet of U-2 spy planes over the large airspace of the then Soviet Union (Russia). On May 1, 1960, one of its high-altitude aircraft was shot down by a Soviet missile, creating great tension between the two superpowers of the time. After this Cold War incident, CIA/DOD decided to move ahead with its space “segment” through the reconnaissance Corona/Key Hole (KH) program. With the deployment of military spacecraft using photographic cameras, whose films are placed in return capsules for mid-air recovery, high-resolution images of the Soviet, Chinese, North Korean, and Cuban territories became a reality. The first successful recovery was thus made with the Discoverer-13 mission on August 19, 1960. The Corona “top secret” imagery was officially declassified in February 1995. It is available from the impressive data center of the US Geological Survey (USGS)/Department of Interior or www.usgs.gov, along with high-resolution multispectral data of other governmental EO satellites.

The impetus for the development of military reconnaissance systems in orbit was provided by the National Reconnaissance Office (NRO) that was created secretly in September 1961. Its creation was kept so secretive that its existence was only revealed to the public, more than 30 years later in 1992! This unit of the DOD is located in Chantilly (Virginia). In September 2011, it celebrated 50 years of vigilance from the sky with a temporary exhibition of “declassified” heavy spacecraft for very high resolution imagery: KH-7/Gambit (1963–1967), KH-8/Gambit-3 (1966–1984), and KH-9/Hexagon (1971–1986) were capable of detecting objects of up to 10 cm in length! For reconnaissance activities from space, some of the US satellites also use opto-electronic systems for digital high-resolution imagery. The Satellite and Missile Observation System (SAMOS) spacecrafts were launched from January 1961 to November 1962. Their modus operandi was to capture an image and to develop the film on board the satellite, and then to scan the image electronically for transmission via telemetry. This last alternative was proven to be unnecessary based on the comparison with the excellent-quality photographic materials collected with recoverable capsules. However, the usage of the SAMOS spacecrafts was particularly useful in going a step forward with the utilization of digital cameras for quickly mapping large territories and isolated areas with great accuracy. To be optimistic, there is a possibility to synchronize the same feature to combine two images to give a three-dimensional (3D) view of the imagery in question.

This 3D vision was demonstrated by a series of Moon mapping observatories, which benefited from access to classified spy satellite technology because of a secret agreement between NASA and the NRO. Five automated Lunar Orbiters were developed and operated by NASA to map the Moon surface for landing sites in preparation of the manned Apollo expeditions. Put into lunar orbit between August 1966 and August 1967, the robots of NASA photographed 99% of the Moon with resolution as low as 1 m for some areas. Their advanced system to take high-quality pictures was provided by an Eastman Kodak camera and derived from instruments designed for the U-2 spy plane. The on-orbit–developed film was scanned by a photomultiplier for transmission to Earth.

Today, photography is a significant player in the digital revolution. The technology used in the camera of a remote sensing satellite is the same technology we have in a digital camera or a cell phone. It uses a charge-coupled device (CCD), which is a form of solid-state electronics similar to the computer chip, which turns light reflectance into an electrical message. Such a technology reduces the mass of the optical sensor and makes it more compact. You may find miniaturized cameras on a small satellite. However, to focus on specific targets for high-resolution pictures, you need to innovate with new types of telescopes. The pioneering EO satellite systems during the 1960s used mostly optical devices for multispectral remote sensing. Their successful development of new applications had to challenge some critical aspects in space: the stability of the platform, the agility of the spacecraft, the quick processing of the imagery, and the corrective action related to the atmospheric disturbances on detailed pictures of precise ground items.

The altitude control of a satellite in orbit is particularly crucial for very high resolution remote sensing from space. The platform of a satellite is equipped with star trackers and reaction wheels (gyroscopes), even with micro-thrusters to point the sensors to the targeted areas. The satellite has to compensate its 7.5 km s^−.1 — in 600 km circular orbit — similar to a photographer panning to snap a moving target. The satellite, to view them and to reveal ground changes (illumination, colors, etc.) from different angles, must be very agile to roll itself to 25° side-to-side and 55° along its path. It has to work as a very reactive photographer to get the best vision of an object of an event. The accuracy of the pointing system is an essential prerequisite to achieve a successful campaign of Earth observations from space. The large quantity of data, acquired with multispectral and, especially, hyperspectral sensors, require powerful recorders or memories to store them on board, as well as ground computers to process them.

Image processing has to consider the fact that Earth’s atmosphere is constantly moving due to thermal gradients within it. The Earth’s atmosphere limits how satellites can record data in several ways. The atmosphere is turbulent not only when there are clouds, fog, smoke, and gas pollution but also with a clear sky during the daytime. Astronomers who observe the sky with high-performance telescopes know the effect of the atmosphere on a perfect vision of a celestial phenomenon. When viewing the stars, we observe the twinkling of starlight that is due to the shimmering effect of the atmosphere. In the same fashion, the atmospheric turbulence puts limits on the accuracy of observations of Earth from orbit. The atmospheric turbulence has a serious effect on the resolution level attained at the decimeter level.

The quality of a satellite image is not determined by a simple resolution value in meters or centimeters. A resolution of 10 cm is probably the best that spy satellites can attain, but that does not come close to reading the headlines or the number plate nor even detecting the golf ball. A 10 cm resolution does not mean that two objects 10 cm apart will always be recognized as two objects and that two objects 8 cm apart will always be recognized as a single larger object. The ability to detect the small gap between two objects will depend on facts such as the Sun’s lighting conditions, the shapes and surfaces of the objects, shadowing in the gap, and the color and sheen contrast between the objects and between them and the gap. A gap of 1 cm between two objects would hardly ever be detected.

Cloud cover is another aspect in the atmosphere that significantly prevents the satellites from taking useful photographs much of the time. In the late 1970s the first radar spy satellite appeared that was able to see through the clouds, both during day and night. NASA tested the first radar satellite with the launch of Seasat in June 1978 to demonstrate the feasibility of a global satellite monitoring of oceanographic phenomena. It was operated, for only a few weeks, until October 1978, when a massive short circuit damaged its electrical system. The Synthetic Aperture Radar (SAR), with “phased array” antenna, transmits beams or pulses of microwave energy — in UHF-band, L-band, C-band, or X-band frequencies — and records the echoes or returning reflections on the ground.

The radar principle is used to form an image by utilizing the time delay of the backscattered signals. This electronically active approach for remote sensing observations needs high-power systems on board the satellites: large panels of solar cells, even nuclear reactors (as was the case for many radar satellites of the former Soviet Union). Outside the military spy satellites of the DODs of the United States, China, Japan, Germany (SAR-Lupe), Italy (dual-use Cosmo-SkyMed), India, and Israel, there are civilian and commercial radar satellites in operation throughout the world: Europe, through ESA, with the European Remote Sensing (ERS) (launched in 1991 and in 1995) and Envisat (still operational since 2002), and Canada with Radarsat (since 1995), Infoterra with TerraSAR-X and TanDEM-X.

1.3. Toward global environmental observers in space

In the mid-1960s, NASA began to plan the deployment, for civilian purposes, of a land remote sensing system. In 1965, the USGS office proposed the idea of a remote sensing satellite program to gather facts about the natural resources of our planet. Concurrently, the US DOD feared that this civilian program would compromise the secrecy of its reconnaissance missions. In 1967, the US Department of the Interior attempted to become the lead agency for such a system by announcing the Earth Resources Observation Satellite (EROS) program, focusing primarily on satellite imagery for mapping and geology. This attempt failed, leaving NASA in its clear role of research and development agency to refine its effort, under the name of the Earth Resources Technology Satellite (ERTS). Referred to as the Landsat system in 1975, it aims at collecting data of 80 m resolution along a 185 km wide swath in four spectral bands that were found particularly useful for geological survey and for environmental monitoring: green (0.5–0.6 µm) for vegetation imaging, red (0.6–0.8 µm) for imaging of man-made objects, blue (0.4–0.5 µm) for deep water imaging, and near-infrared (IR) (0.8–1.1 µm) for vegetation and soil moisture observations. These bands are the key wavelengths for most of the current EO satellites for civilian purposes.

ERTS-1 or Landsat-1 was a modified Nimbus-type meteorological satellite. Launched on July 23, 1972, it heralded a new age of land remote sensing from space. Until then, this dimension was intensively used by meteorological services and by military intelligence. Put in 917 km altitude sun-synchronous orbit, the environmental observatory of NASA remained operational until January 1978. This stabilized, Earth-oriented platform was designed to carry two optical devices: a three-camera Return Beam Vidicon (RBV) system and a four-channel MultiSpectral Scanner (MSS) which acquired some 300,000 images with a resolution of 80 m and with a swath width of 185 km.

Similar to Landsat-1, Landsat-2 and Landsat-3 with MSS and an enhanced vidicon camera were launched in 1975 and 1978 respectively: they demonstrated that NASA has a long-term vision for Earth observation. The main objective of the Landsat program was to make the data widely available to nearly all potential users regardless of political affiliation. During the Cold War, at the opposite end of the secrecy surrounding the military Corona program, Landsat data played an important role in demonstrating the open exchange of information and ideas, for new applications, to the world community. This openness represented a great change in the strategy of the USA in geo-information services. It pushed ahead a political strategy toward global transparency, to face the worldwide changes of life conditions on the “spaceship Earth” with more than 7 billion inhabitants!

In the mid-1970s, NASA began developing the more capable Thematic Mapper (TM), derived from the MSS instrument, for the Landsat-4 and Landsat-5 missions with heavier spacecraft using a new design. This new multispectral sensor collects 30 m resolution data in the visible and the near-IR spectral bands along the same 185 km swath. In 1979, the White House decided that the Landsat system, now ready for operational status, would be transferred for control to the NOAA that operates the geostationary and polar weather satellites of the USA. Because of budgetary constraints and to ensure continuity of Landsat observations, a decision was taken in 1984 to transfer the operational control of the system to a private firm: the Earth Observation Satellite Company (EOSAT) won the competitive bidding process and took over Landsat activities. In the meantime, in 1982, France (along with Belgium and Sweden) decided to go ahead with the commercial SPOT Image company that established as a worldwide distributor of products and services using imagery from the EO satellites. In 1983, SPOT Image opened a subsidiary close to Washington, D.C.

EOSAT had to face a long-term funding dispute among Congress, the federal administration, NOAA, NASA, and the USGS. Even though the US government as a whole was, and still remains, the largest customer for the Landsat-type data, no single agency was willing to commit sufficient operating funds to continue the sustainable management of system operations. At the end of 1992, EOSAT ceased processing the Landsat data. This ...