s i n e

g e t i n s p i r e d

Issue 0.9 (Paper) – November 2001

In this issue

Photogrammetry
Quantum Cascaded Lasers
Interview with Dr. Kumar Easwaran

Acknowledgements

Editor: M. P. Prasad
Designer: Karthik Abhiram
Articles: Manasa Pamaraju, D. Kiran, M. Praveen, M. Chandana

SINE would not have been possible without the support of our Prinicipal, Dr. P. Narasimha Reddy, and the management of SNIST.

Photogrammetry

Definition

Photogrammetry is the science of quantitative analysis of measurements from photographs. Photogrammetry is derived from three Greek words: Photos - light; Gramma - to draw; Metron - to measure. Therefore the root words originally signified measuring graphically by means of light. The complete definition says, “Photogrammetry is the art, science and technology of obtaining reliable information about physical objects and the environment through processes of recording, measuring and interpreting photographic images & patterns of electromagnetic radiant energy and other phenomena.

History

The advent of acquiring airborne photographs and their processing in order to gather information started gaining momentum from the time of World War II. The initial methods of acquiring photos or images from aircrafts using cameras or scanners were interpreted analytically. The four development cycles of Photogrammetry, since the 1850's is outlined below.

· Plane table photogrammetry, 1850 to 1900,

· Analog photogrammetry, 1900 to 1960,

· Analytical photogrammetry, 1960 to present, and

· Softcopy/Digital Photogrammetry

The advent of Digital Photogrammetry widened its user base and number of potential applications. Because of simplicity to handle digital photogrammetry instruments, the level of user training required to produce accurate data is greatly reduced and the Digital Photogrammetry Systems (DPSs) offer a much greater degree of functionality.

Types of Photogrammetry

In principle, Photogrammetry can be divided as follows:

Depend on lens-setting:

· Far range photogrammetry (with camera distance setting to indefinite), and

· Close range photogrammetry (with camera distance settings to finite values).

Another grouping can be:

· Aerial photogrammetry (mostly far range photogrammetry), and

· Terrestrial Photogrammetry (mostly close range photogrammetry).

Benefits of Photogrammetry

· A high level of accuracy that cannot be achieved through any other surveying technique.

· Cost effective due to Minimized Field Time.

· Inaccessible areas can be mapped with ease.

· Results in 3D CAD Format

· The photographs and the generated data can be archived for future use.

Applications

Principally, it is utilized for object interpretation (What is it? Type? Quality? Quantity) and object measurement (Where is it? Structure? Size?). Few applications are listed below:

· Topographic and thematic mapping.

· Land use planning and mapping

· Geological mapping

· Architectural & Archaeological recording

· Digital elevation/terrain models

· Engineering Mapping

· Static and dynamic deformation measurement

· Construction and route planning

Satellite Photogrammetry

Satellite photogrammetry has been a major step forward in the mapping as it facilitates to map large areas with very few images taken by satellites and cost effective compared with aerial photography. Aerial Photogrammetry can be used to scan a particular extent of area and the image specifications like scale, camera, time of photograph etc can be manipulated. But in Satellite Remote Sensing, the satellite orbits are very stable once the satellite has been launched. Aerial Photographs always prevail over satellite imageries for better resolution as 1:5,000 scale of aerial photo is compared with 1:20,000 scale of satellite image. But the repetition of satellite imaging and reliability of obtaining the image in any weather conditions form major advantage of Satellite Photogrammetry.

Conclusions

Photogrammetry is an indigenous technique to obtain reliable scale measurements from aerial photos or satellite imageries. Like any other technology, photogrammetry is also not devoid of limitations. For example, the pipe elevation cannot be obtained for features like underground infrastructure (like sewer lines and others). Also, it is tedious to survey the sites with no details like (open fields) than sites with extensive details. However the latest developments in Photogrammetry paves the way to overcome the above said difficulties. To conclude, Digital Photogrammetry and Satellite Remote Sensing should be used in tandem to exploit the resources for reaping optimal benefits.

- Manasa Pamaraju, EEE III/IV

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Quantum Cascaded Lasers (QCLs)

Nano Science and Technology are rapidly developing fields and one of the major breakthroughs in this field is the QCL.

What is it?

LASER stands for Light Amplification by Stimulated Emission and Radiation. Properties of this new laser depend upon very clever manipulation of electron motion through a system. This new technology allows for more efficient operation and production of laser light over a wide band of frequencies that until now unattainable. These characteristics make the QCL a useful tool for a wide range of applications.

LASERs - Nuts and Bolts

Consider two energy levels E2 and E1 (E2>E1). Initially, consider an electron in E1. When this electron is excited by means of applied voltage or light, it is elevated to E2. An excited electron will not stay in this state for an indefinite amount of time; it will drop back into the ground state and in the process must release energy. This energy will be equal to E2-E1 and will be released in the form of a photon.

In a semiconductor laser, when an electron is elevated from valence band to conduction band, it cannot stay in that state for a long time and hence will drop back to the valence band and in the process release a photon.

The QCL is fundamentally different from a semiconducting laser because it does not utilize recombination of electron-hole pairs to produce photons. Instead, it takes advantages of quantum confinement and Tunneling.

Tunneling: In a forbidden energy region, classically a particle is not allowed to exist. The probability of finding an particle in such a location is zero. In Quantum mechanics, the probability is not instantly zero but decays as a negative potential. So, even though a barrier exists, if the barrier is sufficiently thin, an electron may escape to another allowed state on the opposite side of the forbidden energy region.

Quantum confinement: Confining the movement of an electron from 3-D to 2-D; we can limit the energy states of the electron to very specific values. This forces each electron into quantized energy states. By varying the thickness of the confining region, scientists can specify the value of energy states within the layer. This type of 2-D strip of allowed energy states is a\called a quantum well.

How does it work?

An applied voltage drives electrons. The active layers are repeated up to 75 times and when the voltage is applied, they form an energy staircase. When an electron tumbles down in energy, photons are released at each step.

Applications

The first successful QCL developed at Bell Lab had 25 active regions to produce photons.QCL has important applications in spectral analysis. When QCL of 'n' wavelengths are sent through a mixture of gases and if 'n-m' wavelengths are recorded by the spectrometer, then the gas pertaining to 'm' wavelength is detected. Future applications may include cruise control in poor visibility, medical diagnostics etc.

Conclusion

The versatility and power of QCLs herald a new renaissance for spectral analysis and other wide-ranging real world applications.

- D. Kiran and Praveen, EEE III/IV

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Interview with Dr. Kumar Easwaran

Dr. Kumar Easwaran

Theoretical Physicist by Training and Engineer by Profession

Schooling: Bishop School, Pune
Graduation: Graduated in Mathematics and Science from Jabalpur.
Masters: From I.I.T. Kanpur (1966-1968)
Doctoral Studies: Madras University (1973)
Post Doctoral Studies:

· I.I.T. Delhi

· Research Fellow in Ohio (US Defence Project - Naval Research) (1980s)

Work Experience: Worked in B.H.E.L. R&D as Additional General Manager

What are your Areas of Research?

o Mathematical Technology

o Integral Equations

o Applied Mechanics

o Power Systems

o Electrical Field Theory

What was your Research Topic in Ph.D.?

Quantum Systems (Phase and Coherence)

(Signal Processing) (Field Theory)

What is the approach one has to adopt during research?

o Go through the latest journals.

o Select the areas that interest you.

o Read original papers.

o Reading Reviews is also helpful as it provides insights into the paper and explores the various possible applications.

o Finally, pick up a problem and start working on it.

Where did you enjoy working most (including SNIST)?

The best thing about SNIST is that we get to see fresh faces. But I enjoyed most during my stint at Madras University.

How did you shift to the computers field?

There are only two fields in this world - Mathematics and Physics. Based on this the rest are born. But my introduction to the computer field was through a course that was offered by I.I.T. Kanpur.

What do you think is the technology of the future?

The 21st century belongs to Computer Science and Biotechnology. Communications will also be revolutionised.

In ten years from now, in what direction will the research in Computer Science be oriented?

Hardware will become more versatile, Software is going to be more specific, Applications will become more specialised and even the most complicated software such as that for Image Processing/Pattern Recognition will be available as Packages.

How about Artificial Intelligence?

Well, a breakthrough is required to inculcate thinking in a machine.

What is holding us back from doing so?

Basically, we don't know how we think.

What qualities do you expect in your students?

o They should be sincere to their subject and in their lives.

o Be a student forever. Learning is a continuous process, never stop it.

o Never lose heart.

"Tomorrow is Another Day"

We heard that you guided Doctoral Fellows at I.I.T. Madras. What were the areas of their research?

It was mainly related to Mechanical Engineering on Computer Aided Techniques, and also on Neural Networks.

What are the disciplines on which students can consult you?

o Pattern Recognition

o Image Processing

o Finite Element Method

o Electrical Field Theory

... and of course, anything related to Mathematics.

PERSONAL PROFILE

His father was an Army Officer
His wife Suhasini runs Samaritan High School in Vijaypuri, Mathuranagar
He has two children - daughter Deepti is doing her M.Sc. (Comp.) and his son Akilesh is doing his Doctoral Research in Mathematics at Cambridge University.

- M. Chandana, CSE III/IV

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Watch out for Campus Talk, Brain Teasers in the Concept Clinkers Section…

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