INTRODUCTION

Thermal Energy

Energy can come in many forms, and it can change from one form to another but can never be lost. This is the First Law of Thermodynamics. A byproduct of nearly all energy conversion is heat, which is also known as thermal energy. When there is a temperature difference between two objects or two areas within the same object, heat transfer occurs. Heat energy transfers from the warmer areas to the cooler areas until thermal equilibrium is reached. This is the Second Law of Thermodynamics. When the temperature of an object is the same as the surrounding environment, it is said to be at ambient temperature.

Heat Transfer Mechanisms

Thermal energy transfer occurs through three mechanisms; conduction, convection, and/or radiation. Conduction occurs primarily in solids and to a lesser degree in fluids as warmer more energetic molecules transfers their energy to cooler adjacent molecules. Convection occurs in liquids and gases, and involves the mass movement of molecules such as when stirring or mixing is involved. The third way that heat is transferred is through electromagnetic radiation of energy. Radiation needs no medium to flow through and, therefore, can occur even in a vacuum. Electromagnetic radiation is produced when electrons loose energy and fall to a lower energy state. Both the wavelength and intensity of the radiation is directly related to the temperature of the surface molecules or atoms.

Wavelength of Thermal Energy

The wavelength of thermal radiation extends from 0.1 micron to several hundred microns. As highlighted in the image, this means that not all of the heat radiated from an object will be visible to the human eye… but is detectable. Consider the gradual heating of a piece of steel. With the application of a heat source, heat radiating off of the part is felt long before a change in color is noticed. If the heat intensity is great enough and applied for long enough, the part will gradually change to a red color. The heat that is felt prior to the part changing color is the radiation that lies in the infrared frequency spectrum of electromagnetic radiation.

Infrared (IR) radiation has a wavelength that is longer than visible light or, in other words, greater than 700 nanometers. As the wavelength of the radiation shortens, it reaches the point where it is short enough to enter the visible spectrum and can be detected with the human eye.

An infrared camera has the ability to detect and display infrared energy. Below is an infrared image of an ice cube melting. Note the temperature scale on side, which shows warm areas in red and cool areas in purple. It can be seen that the ice cube is colder than the surrounding air and it is absorbing heat at its surface. The basis for infrared imaging technology is that any object whose temperature is above 0°K radiates infrared energy. Even very cold object radiate some infrared energy. Even though the object might be absorbing thermal energy to warm itself, it will still emit some infrared energy that is detectable by sensors. The amount of radiated energy is a function of the object's temperature and its relative efficiency of thermal radiation, known as emissivity.

Emissivity
A very important consideration in radiation heat transfer is the emissivity of the object being evaluation. Emissivity is a measure of a surface's efficiency in transferring infrared energy. It is the ratio of thermal energy emitted by a surface to that energy emitted by a perfect blackbody at the same temperature. A perfect blackbody only exists in theory and is an object that absorbs and reemits all of the energy. Human skin is nearly a perfect black body as it has an emissivity of 0.98 regardless of actual skin color.

If an object has low emissivity, IR instruments will indicate a lower temperature than the true surface temperature. For this reason most systems and instruments provide the ability for the operator to adjust the emissivity of the object being measured. Sometimes, spray paints, powders, tape or "emissivity dots" are used to improve the emissivity of an object.

Imaging Systems

Thermal imaging instruments measure radiated infrared energy and converts the data to corresponding maps of temperatures. A true thermal image is a gray scale image with hot items shown in white and cold items in black. Temperatures between the two extremes are shown as gradients of gray. Some thermal imagers have the ability to add color, which is artificially generated by the camera's video enhancement electronics, based upon the thermal attributes seen by the camera. Some instruments provide temperature data at each image pixel. Cursors can be positioned to each point with the corresponding temperature read out on the screen or display. Images may be digitized, stored, manipulated, processed and printed out. Industry-standard image formats, such as the tagged image file format (TIFF), permit files to work with a wide array of commercially available software packages.

Images are produced either by scanning a detector or group of detectors, or by using with focal plane array. A scanning system in its simplest form, could involve a single element detector scanning along each line in the frame (serial scanning). In practice, this would require very high scan speeds so a series of elements are commonly scanned as a block, along each line. This cuts down the scan speed from having just a single detector but the scan speed and channel bandwidth requirements are still high. It does, however, give a good degree of uniformity. The frame movement can be provided by frame scanning optics (using mirrors) or in the case of linescan type imagers, by the movement of the imager itself. Another method is to use a number of elements scanning in parallel (parallel scanning). These have one element per line but scan several lines simultaneously. Frame scan speeds are lower but this method can give rise to poor uniformity.

FOCAL PLANE ARRAY

Another way thermal images are produced is with a focal plane arrays (FPA) (or staring array). A focal plane array is a group of sensor elements organized into a rectangular grid. A high magnification image of a portion of a micro bolometer focal plane array is shown to the right. The entire scene is focused on the array; each element cell then provides an output dependent upon the infrared radiation falling upon it. The spatial resolution of the image is determined by the number of pixels of the detector array. Common formats for commercial infrared detectors are 320x240 pixels (320 columns, 240 rows), and 640x480. The latter format is nearly the resolution obtained by standard TV. Spatial resolution, the ability to measure temperatures on small areas, can be as fine as 15 microns. Temperature resolution, the ability to measure small temperature differences, can be as fine as 0.1° C. Temperature sensitivity and measurement range cover broad ranges.

The advantage of FPAs is that no moving mechanical parts are needed and that the detector sensitivity and speed can both be slower. The drawback is that the detector array is more complicated to fabricate and manufacturing costs are higher. However, improvements in semiconductor fabrication practices are driving the cost down and the general trend is that infrared camera systems will be based on FPAs, except for special applications. A micro bolometer is the latest type of thermal imaging FPA, which consists of materials that measure heat by changing resistance at each pixel. The most common micro bolometer material is vanadium oxide (VOx). Amorphous silicon is another relatively new micro bolometer material.

Applications extend from microelectronic levels to scanning wide areas of the earth from space. Airborne systems can be used to see through smoke at forest fires. Portable, hand-held units can be used for equipment monitoring in preventative maintenance and flaw detection in nondestructive testing programs.

Equipment for Establishing Heat Flow

In some inspection applications, such as corrosion or flaw detect, the components being inspected may be at ambient temperature and heat flow must be created. This can be accomplished by a variety of means. Heating can be accomplished by placing the part in a warm environment, such as a furnace, or directing heat on the surface with a heat gun or with flash lamps. Alternately, cooling can be accomplished by placing the component in a cold environment or cooling the surface with a spray of cold liquid or gas.

Image Capturing and Analysis

IR camera alone or used with an external heat source can often detect large, near-surface flaws. However, repeatable, quantifiable detection of deeper, subtler features requires the additional sensitivity of a sophisticated computerized system. In these systems, a computer is used to capture a number of time sequence images which can be stepped through or viewed as a movie to evaluate the thermal changes in an object as a function of time. This technique is often referred to as thermal wave imaging.

The image to the right shows as pulsed thermography system. This system uses a closely controlled burst of thermal energy from a xenon flash lamp to heat the surface. The dissipation of heat is then tracked using a high speed thermal imaging camera. The camera sits on top of the gray box in the foreground. The gray box houses the xenon flash lamp and it is held against the surface being inspected. The equipment was designed to inspect the fuselage skins of aircraft for corrosion damage can make quantitative measurements of material loss. It has also been shown to detect areas of water incursion in composites and areas where bonded structure has separated.

Sea Surface Temperature

Instruments aboard NASA's and NOAA's spacecrafts use their vantage point from space to collect global measurements of the ocean's surface temperature. Each day these instruments make thousands of measurements of broad swaths of the Earth - creating concurrent data sets of the entire planet. By developing global, detailed and decades-long views of Sea Surface Temperature (SST), data obtained from NASA and NOAA satellites provide the basis for the prediction of climate change, ocean currents, and the potent El Niño-La Niña cycles.

El Niño is perhaps the best known example of the impact that changing sea surface temperature has on our climate. Every three to seven years, this warming of surface ocean waters in the eastern tropical Pacific brings winter droughts and deadly forest fires in Central America, Indonesia, Australia, and southeastern Africa, and lashing rainstorms in Ecuador and Peru. El Niño affects thousands of people worldwide, and billions of dollars in economic impact. El Niño's "sister," La Niña, occurs less frequently and has the opposite effect - the cooling of surface ocean waters.

But changing SST patterns have broader implications than just the El Niño and La Niña cycles. Changes in SST are the single most important indicator of climate change. Heat is one of the main drivers of global climate, and the ocean is a huge reservoir of heat. The top 6.5 feet of ocean has the potential to store the equivalent amount of heat contained in the atmosphere. The ocean has a high capacity and as ocean currents move tremendous amounts of water over vast distances, heat is also carried or transferred over these distances. This release of heat can play a major role in climate from the regional/basin to global scale. It is for this reason that oceans are termed the 'memory' of the Earth's climate system. Tracking SST as a variable over long periods of time, as well as operationally, is critical for developing climate models and improved weather forecasts.

Every day the Moderate-resolution Imaging Spectroradiometer (MODIS) measures sea surface temperature over the entire globe with high accuracy. This false-color image shows a one-month composite for May 2001. Red and yellow indicates warmer temperatures, green is an intermediate value, while blues and then purples are progressively colder values.

The distribution of temperature at the sea surface tends to be zonal, that is, it is independent of longitude. Uneven heating of the Earth by the Sun causes the warmest water to be near the equator, while the coldest water is near the poles. The deviations from these zonal measurements are small.

The anomalies of sea-surface temperature, the deviation from a long term average, are also small, less than 1.5°C/34.7°F except in the equatorial Pacific where the deviations can be 3°C/37.4°F. Large deviations in the Equatorial Pacific are due primarily to the El Niño-La Niña cycle.

Most weather and climate events are the result of sea and atmospheric coupling. Heat energy released from the ocean is the dominant driver of atmospheric circulation and weather patterns. SST influences the rate of energy transfer into the atmosphere, as evaporation increases rapidly with temperature. Knowing the temperature of the ocean surface provides tremendous insight into short and long term weather and climate events.

Temperature as measured by the NASA Aqua satellite's Advanced Microwave Scanning Radiometer (AMSR-E) instrument. Temperature is represented by the colors in the ocean. Orange and red indicate the necessary 27.7°C/82°F and warmer sea surface temperatures for a hurricane to form.

This visualization was match-frame rendered to another visualization showing clouds. This visualization was created in support of the Recipe for a Hurricane feature story.

Taking the Ocean's Temperature

The most commonly used instrument to measure sea-surface temperature from space is the Advanced Very High Resolution Radiometer AVHRR. Since 1999, the Moderate-resolution Imaging Spectroradiometer (MODIS) sensor has been collecting even more detailed measurements of surface temperature. More recently, the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) has been collecting SST that includes areas covered by clouds. A key attribute of the AVHRR data is the length of the time record.

An AVHRR sensor has been carried on all polar-orbiting meteorological satellites operated by NOAA since Tiros-N was launched in 1978. High quality measurements of the temperature of the ocean are now available from 1981 to the present. This unique SST data set is now the longest satellite derived oceanographic record, providing a 25-year (and continuing) record of global SST changes. Conversely, MODIS and records are much shorter.
Sea surface temperature data are used to help us predict weather patterns, to track ocean currents, and to monitor El Niño and La Niña. Sea surface temperature influences the growth of phytoplankton, as well as precipitation patterns across continents, thus indirectly influencing land vegetation. (Data from Advanced Very High Resolution Radiometer [AVHRR])

Thermal Infrared Remote Sensing

AVHRR and MODIS instruments use radiometers to measure the amount of thermal infrared radiation given off by the surface of the ocean. Thermal infrared remote sensing is based on the fact that everything above absolute zero (-273°C/459°F) emits radiation in the thermal infrared region of the electromagnetic spectrum. The amount of thermal infrared radiation given off by an object is related to its temperature (dying embers give off less radiation than a hot fire). Thus by measuring the amount of radiation given off by the ocean we can calculate its temperature. With instruments like radiometers, it is possible to get a picture of the thermal environment that we cannot experience with our normal human sensors. The ability to record precise variations in infrared radiation has tremendous application in extending our observation of many types of phenomena where minor temperature variations are significant in understanding our environment.

Advanced Very High Resolution Radiometer

The AVHRR five channel scanning radiometer with 1.1-km resolution is sensitive in the visible and near-infrared, and the infrared 'window' regions. This instrument will be carried through NOAA-J (14); NOAA-K, L and M (15, 16, and 17) and will have a similar instrument with six channels and other improvements. AVHRR data are broadcast for reception by ground stations and also tape-recorded onboard the spacecraft for readout at the Fairbanks and Wallops Command Data Acquisition stations. These data can be recorded in 1.1-km resolution (the basic resolution of the AVHRR instrument) or at 4 km resolution; the swath width is >2600 km. The stored high resolution (1.1-km) imagery is known as Local Area Coverage (LAC). Owing to the large number of data bits, only about 11+ minutes of LAC can be accommodated on a single recorder. In contrast, 115 minutes of the lower resolution (4-km) imagery, called Global Area Coverage (GAC), can be stored on a recorder, enough to cover an entire 102 minute orbit of data.

The AVHRR has flown on the following U.S. civilian meteorological satellites: TIROS-N; NOAA-6 through NOAA-14, inclusive.

NOAA-K, L and M (NOAA-15 onwards) carry an enhanced version of the AVHRR scanner. It has six channels (three visible and three infra-red) but, for compatibility at receiving stations, only five are transmitted. Channel 3 is the visible channel during the daytime and the infra-red channel at nighttime. Additionally, the visible channels have been modified with a dual slope for calibration to give greater sensitivity at low light levels.

Channel	Wavelength (microns)	Primary Use
1	0.58 - 0.68	Daytime cloud/surface mapping
2	0.725 - 1.10	Surface water delineation, ice and snow melt
3A	1.58 - 1.64	Snow / ice discrimination (NOAA K,L,M)
3B	3.55 - 3.93	Sea surface temperature, nighttime cloud mapping
4	10.30 -11.30	Sea surface temperature, day and night cloud mapping
5	11.50 -12.50	Sea surface temperature, day and night cloud mapping

Background

The Advanced Very High Resolution Radiometer (AVHRR) data set is comprised of data collected by the AVHRR sensor and held in the archives of the U.S. Geological Survey’s EROS Data Center. Carried aboard the National Oceanic and Atmospheric Administration’s (NOAA) Polar Orbiting Environmental Satellite series, the AVHRR sensor is a broad-band, 4- or 5-channel scanning radiometer, sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum.

The EROS Data Center houses AVHRR High Resolution Picture Transmission (HRPT) data and Local Area Coverage (LAC) data. The HRPT data are full resolution image data transmitted to a ground station as they are collected, while LAC data (also full resolution data) are recorded with an onboard tape recorder for subsequent transmission during a station overpass. The objective of the AVHRR instrument is to provide radiance data for investigation of clouds, land-water boundaries, snow and ice extent, ice or snow melt inception, day and night cloud distribution, temperatures of radiating surfaces, and sea surface temperature. The AVHRR data collection effort also provides opportunities for studying and monitoring vegetation conditions in ecosystems, including forests, tundra, and grasslands with applications that include agricultural assessment, land cover mapping, production of large-area image maps and evaluation of regional and continental snow cover.

Extent of Coverage

The AVHRR sensor provides for global (pole to pole) on board collection of data from all spectral channels. Each pass of the satellite provides a 2399 km (1491 mi) wide swath. The satellite orbits the Earth 14 times each day from 833 km (517 mi) above its surface.

Acquisition

The EROS Data Center (EDC) AVHRR Data Acquisition and Processing System (ADAPS), which began operation in May 1987, receives approximately six daytime passes per day of HRPT data over the conterminous United States. Night acquisitions are acquired upon request only. As of March 1990, all data received at EDC are permanently archived. Prior to March 1990, approximately 40 percent of the data received were archived. The EROS Data Center AVHRR Data Acquisition and Processing System was expanded on June 15, 1990, to acquire LAC data via a communications satellite for areas recorded throughout the entire globe. Priority is given to LAC acquisitions of the North American continent not covered by EDCs direct reception. NOAA/NESDIS receives both world-wide recorded and direct readout AVHRR data from the Wallops Island, Virginia, and Gilmore Creek, Alaska, stations. These stations then redirect the data via a satellite relay to NOAA/National Environmental Satellite, Data and Information Services in Suitland, Maryland, where the data are processed, archived, and reproduced. The EROS Data Center ADAPS system was reconfigured in July of 1997 to acquire LAC via electronic transfer from NOAA/NESDIS, replacing the DOMSAT communications link.

Applications and Related Data Sets

AVHRR data provide opportunities for studying and monitoring vegetation conditions in ecosystems including forests, tundra, and grasslands. Applications include agricultural assessment, land cover mapping, producing image maps of large areas such as countries or continents and tracking regional and continental snow cover. AVHRR data are also used to retrieve various geophysical parameters such as sea surface temperatures and energy budget data.

Additional data sets include the Alaska twice-monthly AVHRR and the U.S. Conterminous bi-weekly composites. These comprehensive time series data sets are calibrated, georegistered daily observations and twice-monthly maximum NDVI composites for each annual growing season.

Global Experimental Bi-Weekly Normalized Difference data, computed from Global Vegetation Index (GVI) data, are analyzed to monitor global vegetation as a potential tool in global climatic studies.

Moderate-resolution Imaging Spectroradiometer

MODIS is sensitive to five different wavelengths, or "channels," of radiation used for measuring SST. Both night and day, the sensor measures the thermal infrared energy escaping the atmosphere at 12 microns and then compares that measurement to how much energy is escaping at 11 microns, allowing scientists to determine how much the atmosphere modifies the signal so they can "correct" the data to more accurately derive SST. The MODIS sensor, because of the increased number of channels, tells us a great deal about the influence of the atmosphere on measurements of SST. Similar to AVHRR, MODIS also takes daily measurement of the global ocean. The oceans are a dynamic and exciting environment. But they are not a single environment in themselves. Rather, they interact with the atmosphere, land, ice, and living things.

Global productivity of the land and oceans for 2002,
as derived from MODIS measurements

They are part of the interconnected systems of the Earth. Furthermore, humans influence the oceans and are also influenced by them. To help understand these interrelationships, scientists are using measurements from space-based instruments, such as MODIS.

This tutorial describes how the MODIS instrument is used in scientific research about the oceans.

What is MODIS?

MODIS, or Moderate Resolution Imaging Spectroradiometer, is an instrument on two satellites that circle the Earth. The satellites are called Terra and Aqua. These satellites look down at the Earth and make measurements to help scientists better understand the environment.

MODIS instrument

MODIS measures light from the Earth's surface at different wavelengths. This kind of instrument is known as a spectroradiometer. MODIS can measure light at both visible and infrared wavelengths. Visible light wavelengths can be seen by the naked eye. On the other hand, infrared, an indicator of heat, cannot be seen by the naked eye. Like a digital camera that records visible light wavelengths, MODIS can be considered a digital camera in space that takes pictures of the Earth surface in visible and infrared wavelengths at the same time. There are 36 different wavelengths that MODIS measures. With this capability, MODIS can create images of phenomena that the naked eye can't see.

The name, "Moderate Resolution", indicates that the ocean images have a spatial resolution of one kilometer. The spatial resolution is the size of the smallest distinguishable object on the ground that can be seen by the instrument. Stated another way, each picture element (or pixel) of a MODIS ocean image is one square kilometer in area. MODIS's moderate spatial resolution is much more coarse than some other satellites like Landsat or spy satellites. With a spatial resolution that is not too detailed, a picture of almost the entire Earth can generated each day.

MODIS on Terra and Aqua

Terra and Aqua are satellites of NASA's Earth Observing System. Both satellites look down at the Earth surface from an altitude of 438 miles (705 km). From this vantage point, scientists can gain an understanding of various aspects of the Earth. The Earth is an interrelated system. The atmosphere, hydrosphere, lithosphere, cryosphere and biosphere all work in conjunction. By looking at the Earth from space, a picture of the whole Earth with its various interrelated systems can be obtained.

TERRA AQUA

MODIS is one of five instruments on the Terra satellite and one of six instruments on the Aqua satellite.

Both Terra and Aqua circle the Earth from pole to pole, fourteen times per day. Each orbit takes about 100 minutes. In this way, Terra and Aqua can each scan most of the Earth surface in a single day. When on the daylight side of the Earth, Terra follows an orbit from the North Pole to the South Pole. Aqua, on the otherhand, follows an orbit from the South Pole to the North Pole. Thus, Terra and Aqua are circling the Earth in opposite directions!

When Terra crosses the equator on the daylight side of the Earth, it is always approximately 10:30 AM local time. For Aqua, the equator-crossing time is always approximately 1:30 PM locally. The local time is the same from orbit to orbit (for each satellite) because the Earth is rotating as the satellites are circling.

As a result, the Terra data always represent morning conditions, and the Aqua data always represent afternoon conditions. Thus, scientists can use MODIS data from Terra and Aqua to see how the Earth changes from morning to afternoon.

What can MODIS see about the oceans? Water temperature!

MODIS can see the temperature of the surface water of the ocean. This sea surface temperature is calculated from MODIS's infrared wavelength channels. The below image of sea surface temperature shows where the temperature of the surface ocean is hottest and coolest. The red colors are the hottest temperatures (30 degrees Celsius on the color scale), and the purple and blue colors are the coolest temperatures (0 degrees Celsius on the color scale).

The oceans have immense capacity to store heat. Therefore, the oceans have a strong effect on the Earth's climate.

Notice that the hottest ocean temperatures occur around the equator, and the coolest near the north and south poles. This is because the sun is warming the Earth the most at the equator. The oceans then transport the heat toward the poles. Notice the Gulf Stream off the east coast of North America. It is a warm current that transports heat from the warm tropical waters to the cooler temperate waters.

Also notice the cooler waters (green color) at the equator just west of South America. These waters are cooler because of upwelling currents that bring ocean water from depths where the water is cooler. Through the transport of heat across the Earth's surface, the oceans moderate climate on Earth. Scientists are using the sea surface temperatures from MODIS to gain a better understanding of how the ocean currents moderate climate.

What can MODIS see about the oceans? Color!

MODIS can see the color of the surface water. Varying shades of blue and green color tell scientists how much chlorophyll is in the water. Chlorophyll is a pigment that reflects green light, making the ocean water look more green where there is more chlorophyll. Chlorophyll is produced by living single-celled plants in the ocean called phytoplankton. The phytoplankton use chlorophyll to capture sunlight and turn the sun's energy into food. This process is called photosynthesis.

The red colors in the image below show where there is more chlorophyll in the water (chlorophyll concentration > 10 mg/m3 on the color scale) and the blue colors show where there is less chlorophyll in the water (chlorophyll concentration < 0.1 mg/m3 on the color scale). Notice that most chlorophyll occurs near coasts. This is because nutrients are being washed into the oceans from the land. The phytoplankton use the nutrients to grow, thereby producing more chlorophyll. Notice also the green bands of higher chlorophyll at the equator. This occurs because the upwelling currents bring nutrients from the deeper ocean waters to the surface. The phytoplankton grow well in these nutrient-rich waters.

Waste products from human agricultural and industrial practices are washed via rivers to the coastal ocean waters. These wastes are rich in nutrients. If too much waste ends up in the coastal ocean, phytoplankton can overproduce. This is called a phytoplankton bloom. When the phytoplankton of the bloom die, the bacteria of decay decompose the dead phytoplankton cells but use all the oxygen in the water in the decomposition process. This starves other organisms such as fish of the oxygen they need. Many organisms can die as a result of a phytoplankton bloom. Fish kills are massive die-offs of fish, often caused by oxygen depletion in the water. This is especially disastrous in coastal ocean waters because these waters are usually very biologically productive. Humans depend on the fish caught in coastal waters. If there are fish kills, then humans (and other organisms) have less fish to eat. In addition, some phytoplankton produce toxic substances. If there are too many harmful phytoplankton, the toxins end up in the fish and shellfish that humans eat, and humans can become sick or can die. Such blooms are called harmful algal blooms. Satellites can be used to track phytoplankton blooms, to see what coastal areas could be affected.

As phytoplankton grow, they make food in the form of organic carbon, using the sun's energy and carbon dioxide (photosynthesis). In the water, the carbon dioxide is in a dissolved form (carbonate and other ions). This carbon dioxide got into the ocean by dissolving from the atmosphere. Scientists are trying to understand the degree to which phytoplankton utilize the dissolved carbon dioxide in the water, thereby causing more carbon dioxide from the atmosphere to dissolve in the water. As the phytoplankton die, they either decompose in the water, or settle to the bottom of the ocean. This settling causes carbon to be stored at the bottom of the ocean.

Since humans are adding more and more carbon dioxide into the atmosphere through the burning of fossil fuels, it is important to understand where this carbon dioxide goes. Scientists believe that some of the human-produced carbon dioxide is stored in the ocean in the form of phytoplankton growth and settling, but no one yet knows how much the phytoplankton are moderating the amount of atmospheric carbon dioxide.

Advanced Microwave Scanning Radiometer for EOS (AMSR-E)

Because AVHRR and MODIS cannot observe the ocean when the atmosphere is cloudy, NASA developed a new sensor, AMSR-E, that is able to observe through the clouds.

AMSR-E on the Aqua satellite is a passive microwave radiometer, modified from the Advanced Earth Observing Satellite-II (ADEOS-II). Microwaves are radio waves that are able to pass through clouds. Thus, the AMSR-E instrument can measure radiation from the ocean surface through most types of cloud cover, supplementing infrared based measurements of SST that are restricted to cloud-free areas.

However, the resolution of AMSR-E is coarser than the thermal IR sensors. The addition of AMSR-E data will provide a significant improvement in our ability to monitor SST and temperature controlling phenomenon.

The temperature of the world's ocean surface provides a clear indication of the regions where hurricanes and typhoons form, since they can only form when the sea surface temperature exceeds 27.8°C (82°F). In this visualization of AMSR-E data covering the period from June, 2002 to September, 2003, areas with surface temperatures greater than 82°F are shown in yellow and orange, while sea surface temperatures below 82°F are shown in blue.

The region in the Atlantic from the Caribbean to the equator only exceeds the critical temperature during late summer and early fall in the Northern Hemisphere, the period known as "Hurricane Season."

It is also possible to see the Gulf Stream, the warm river of water that parallels the east coast of the United States before heading towards northern Europe, in this data. Around January 1, 2003, a cooler-than- normal region of the ocean appears just to the west of Peru as part of an La Niña and flows westward, driven by the trade winds.

The waves that appear on the edges of this cooler area are called tropical instability waves and can also be seen in the equatorial Atlantic Ocean at about the same time.

Sea Surface Height & Temperature

Sea surface height data can also provide clues to studying the temperature of the ocean. Warm water expands raising the sea surface height. Conversely, cold water contracts lowering the height of the sea surface. Thus, measurements of sea surface height can provide information about the heat content of the ocean. The height can tell us how much heat is stored in the ocean water column below its surface. Learn more about sea surface height.

Interpreting Sea Surface Temperature Measurements

Radiation observed by AVHRR and MODIS is modified by its passage through the atmosphere. The degree to which the signal is modified depends upon the chemistry of the overlying atmosphere. Clouds, haze, dust or smoke can interfere with a space-based remote sensor's ability to accurately measure SST, as can greenhouse gases, like water vapor. These are present in abundance in the tropics and strongly absorb infrared energy and re-radiate it back toward the surface. Scientists have created several algorithms to correct the impact of these variables creating more accurate measurements of SST.

Further, scientists analyze SST data to provide new products that have a wide variety of uses. SST data are also distributed and processed by several organizations. These data sets are then used operationally by sponsoring agency scientists and other organizations.

The Goddard Earth Sciences Data and Information Services Center (GES DISC) at CaltTech/JPL are the key distribution point for SST data and related data sets from NASA.

The Goddard Distributed Active Archive Center (GDAAC) is the primary distribution center for MODIS data.

The Global Hydrology & Climate Center provides browse images and some Level 2 AMSR-E data products.

The GES DISC is the mirror site for the level 3 data sets.

SST data is also combined with other data taken in-situ by ships and bouys. This data helps calibrate the satellite data to create a more accurate measurement of SST.

SST data is used by many different organizations for regional studies, anomaly studies, climate and meteorological studies, and to provide near real - time access to the data. SST data products are also widely used by the fishing industry to track the conditions where fish are most likely to be found.

Long term averages of sea surface temperature are used to calculate the normal seas surface temperature conditions for a specific time of year and location. Deviations from the long-term mean are called anomalies. The long-term means are also used for studying climate change. Other data is made available in time intervals of less than a day - in some instances within a few hours of collection. This type of data is mostly used for detecting specific features in the ocean, such as currents and eddies.

Trends we observe

SST data is used to observe many regional phenomena around the world, including the Chesapeake Bay and the Gulf of Mexico, the Gulf Stream, Kuroshio, the Somali Current, the Brazil Current and the East Australian Current. These currents are associated with sharp changes in SST which can be detected using satellites. Coastal water studies are made off the Hawaiian and Alaskan coasts. Multiple studies are also conducted off the North Atlantic.

The Gulf Stream, one of the ocean's most significant and fastest currents moves at four miles per hour. This current of warm water, which is called the North Atlantic Drift after it turns offshore at Cape Hatteras, travels from the Gulf of Mexico to northern European waters.

The current's warm waters are responsible for the more temperate climates experienced by Ireland, England, Scotland, and the Isles of Scily. At the beginning of the Current, in the Gulf of Mexico, its temperature is around 27°C (80°F), but by the time it reaches northern Europe it has cooled down to a few degrees Fahrenheit. As it cools, it gives up heat to the atmosphere, which carries the warmth to Europe.

This false-color Terra/MODIS image produced from Direct Broadcast data by the Space Science and Engineering Center at the University of Wisconsin-Madison is made from data on Band 31. Its bright colors represent temperature data of the water: the Gulf Stream is shown in shades of orange and yellow, which puts it near 20°C (68°F) on the scale provided in the image. Land temperature data are not shown in this image and appear black, while white represents areas where no data were collected (because clouds obscured the water).

The colder waters off of the coasts of Virginia, Maryland, Delaware, and New Jersey contrast sharply with the warmer waters of the Gulf Stream in this image from March 15, 2005. Credit: SSEC University of Wisconsin - Madison

Sea surface temperatures in the equatorial Pacific affect precipitation (and therefore plant growth) over much of the North American continent. Warmer-than-normal water in the central and western equatorial Pacific, creates higher precipitation in southern and central North America. Conversely, cold water temperatures in the Pacific lead to a decrease in precipitation over northern North America.

SST may also affect one of the world's key large-scale atmospheric circulations - the circulation that regulates the intensity and breaking of rainfall associated with the South Asian and Australian monsoons.

Projects are underway that combine data from multiple satellite systems to produce a robust set of sea surface data for assimilation into ocean forecasting models of the waters around Europe and also the entire Atlantic Ocean. The Global Ocean Data Assimilation Experiment, GODAE, is assimilating sea-surface temperature data, altimeter data, scatterometer data, and drifter data into coupled ocean/atmosphere numerical models to produce forecasts of ocean currents and temperatures up to 30 days in advance everyehwere in the ocean.

APPLICATIONS

Techniques and Select Industrial Applications of Thermal Imaging

Some thermal imaging techniques simply involve pointing a camera at a component and looking areas of uneven heating or localized hot spots. The first two example applications discussed below fall into this category. For other applications, it may be necessary to generate heat flow within the component and/or evaluate heat flow as a function of time. A variety of thermal imaging techniques have been developed to provide the desired information. A few of these techniques are highlighted below.

Electrical and Mechanical System Inspection

Electrical and mechanical systems are the backbone of many manufacturing operations. An unexpected shutdown of even a minor piece of equipment could have a major impact on production.

Since nearly everything gets hot before it fails, thermal inspection is a valuable and cost-effective diagnostic tool with many industrial applications.

With the infrared camera, an inspector can see the change in temperature from the surrounding area, identify if it is abnormal and predict the possible failure. Applications for infrared testing include locating loose electrical connections, failing transformers, improper bushing and bearing lubrication, overloaded motors or pumps, coupling misalignment, and other applications where a change in temperature will indicate an undesirable condition. Since typical electrical failures occur when there is temperature rise of over 50°C, problems can be detected well in advance of a failure.

The image on the right above, shows three electrical connections. The upper right connection is hotter than the others. Connections can become hot if they are loose or if corrosion causes an increase in the electrical resistance.

Corrosion Damage (Metal Thinning)

IR techniques can be used to detect material thinning of relatively thin structures since areas with different thermal masses with absorb and radiate heat at different rates. In relatively thin, thermally conductive materials, heat will be conducted away from the surface faster by thicker regions. By heating the surface and monitoring its cooling characteristics, a thickness map can be produced. Thin areas may be the result of corrosion damage on the backside of a structure which is normally not visible. The image to the right shows corrosion damage and disbonding of a tear strap/stringer on the inside surface of an aircraft skin. This type of damage is costly to detect visually because a great deal of the interior of the aircraft must be disassembled. With IR techniques the damage can be detected from the outside of the aircraft.

Electronic Component Inspection

In electronics design and manufacturing, a key reliability factor is semiconductor junction temperature. When operating, a semiconductor generates heat and this heat will flow from the component. The heat will flow from the component anyway it can but flow particularly well along the thermally conductive connectors. This leads to an increase in temperature at the junctions where the semiconductor attaches to the board. Components with high junction temperature typically have shorter life spans. Thermal imaging can be used to evaluate the dissipation of heat and measure the temperature at the junctions.

Flaw Detection

Infrared techniques can be used to detect flaws in materials or structures. The inspection technique monitors the flow of heat from the surface of a solid and this flow is affected by internal flaws such as disbonds, voids or inclusions. Sound material, a good weld, or a solid bond will see heat dissipated rapidly through the material, whereas a defect will retain the heat for longer.

A new technique call vibrothermograph or thermosonic testing was recently introduced by researchers at Wayne State University for detection of cracks. A solid sample is excited with bursts of high-energy, low-frequency acoustic energy. This causes frictional heating at the faces of any cracks present and hotspots are detected by an infrared camera.
Despite the apparent simplicity of the scheme, there are a number of experimental considerations that can complicate the implementation of the technique. Factors including acoustic horn location, horn-crack proximity, horn-sample coupling, and effective detection range all significantly affect the degree of excitation that occurs at a crack site for a given energy input.

Below are two images from an IR camera showing a 0.050" thick 7075 aluminum plate sample with a prefabricated crack being inspected using a commercial vibrothermography system. The image on the left is the IR image with a pre-excitation image subtracted. A crack can be seen in the middle of the sample and just to the right of the ultrasonic horn. Also seen is heating due to the horn tip, friction at various clamping sites, reflection from a hole at the right edge of the sample. The image on the right is the same data with image processing performed to make the crack indication easier to distinguish.

Future Scope

Finally, projects are also being conducted to combine SST data from various sensors to create the highest quality SST. These projects will create a new generation of multi-sensor, high-resolution SST products. An example of such a project is the GODAE High Resolution Sea Surface Temperature Pilot Project (GHRSST-PP).

SST data are important to the development and testing of a new generation of computer models in which the interacting processes of the land, the atmosphere, and the oceans are coupled. The measurements are widely used in the creation of more accurate weather forecasts and increasingly it is seen as a key indicator of climate change. It is anticipated that projects like GHRSST will provide even higher quality data sets for such things as hurricane forecasting.

Projects like GHRSST lay the groundwork for future cooperations, between NASA and NOAA, as well as internationally. Such cooperations will lead to major innovations in how data is distributed in near real-time, searched and stored. Plans include a joint NASA/NOAA effort to provide users with an interface for accessing both near real-time and historical data for climate studies. Future technologies should allow managers, decision makers, and modelers to search and access data in near real time for specified areas of interest. Additionally, the merging of SST data from different sensors will provide high resolution SST data suitable for coastal studies and management.

Conclusion

Since there is always scope of improvement in any system/device, keeping it in mind it was thought to study about “Thermo scope”. For this purpose I choose this topic for my seminar, it was also useful for me because it is much related to instrumentation.

In this I mainly concentrate on Sea Surface temperature Measurement because it is very advance technology and useful for human being indirectly.

At the end I would like to thanks my seminar guide, our coordinator and all my friends who help me in preparing my seminar.

Bibliography

Websites: