GS 5102 Introduction to Remote Sensing Time 09

GS 5102: Introduction to Remote Sensing Time: 09. 00 – 12. 00 on Saturdays

Course Outline • • • Introduction The history and development of remote sensing, basic definitions, the remote sensing system, aerial photography, satellite remote sensing and their applications. Basic Principles of Electromagnetic Energy The electromagnetic spectrum, electromagnetic sources, the role of electromagnetic energy in remote sensing Remote Sensors Aerial sensors, satellites and their characteristics, land oriented systems and meteorological satellites, satellite sensors and their characteristics, pixels and pixel properties, spatial, spectral, radiometric and temporal resolutions.

Course Outline • • • Digital Image Processing Image file formats, colour composites, band mathematical operations, contrast stretching, radiometric and geometric correction, image enhancement. Image Interpretation of aerial photographs and satellite images, visual and digital interpretation, supervised and unsupervised classification. Laboratory Sessions Visual and digital analysis of remote sensing images and the applications.

What is Remote Sensing? The science and art of obtaining information of an object, area or phenomenon at a distance • Aerial Photography • Satellite Remote Sensing Optical Microwave

Remote Sensing – Data Acquisition Sensor Energy Source Atmosphere Earth Surface

The History • Remote sensing with kites, balloons and pigeons • Development of Aerial Photography – During World War I& II – Military reconnaissance tool – Between World Wars – Non military applications – After 2 nd world war – development of photogrammetry • Spatial Era – 1957 – Spoutnik – 1960 – First image from meteorological satellite TIROS – July, 1972 – ERTS I (Renamed Landsat I)

Electro-magnetic Radiation • The EM spectrum

Electro-magnetic Radiation • Atmospheric Effects – Refraction – Absorption • Atmospheric Transparency – Windows • Absorption by other environments crossed by the EM radiation – Diffusion

Atmospheric Windows • Atmospheric Transparency – The wave length ranges in which the atmosphere is particularly transmissive of energy. – Atmospheric windows correspond to spectral bands for which transmission is relatively high. – Dry atmospheres are more transparent than wet atmospheres.

Atmospheric Windows

EM Radiation – Object Interactions • Reflectance gives an idea about the characteristics of the natural surfaces. • Spectral response measured over objects permits an assessment of the type and condition of them. • These responses are called ‘ Spectral Signatures” • These responses are not absolute or unique. • Spectral response patterns can be changed due to spatial and temporal effects.

Remote sensors record electromagnetic radiation emitted or reflected from the Earth’s surface. Different types of vegetation, soils and other features emit and reflect energy differently. This characteristic makes it possible to identify different cover types on the surface. Using multi-temporal images it is possible to monitor the changes.

EM Radiation – Object Interactions • Vegetation – In visible spectrum • Radiation is absorbed by leaf pigments for photosynthesis (chlorophyll) • Main pigments are Chlorophyll a & b with two absorption bands in blue and red – In NIR • Leaf pigments and the cellulose containing walls are transparent. • High levels of reflectance from vegetation – In MIR • Reflectance is affected by the water content

EM Radiation – Object Interactions

EM Radiation – Object Interactions • Soil – Reflectance increases regularly from visible to NIR – Absorption bands due to water (1. 4 mm & 1. 9 mm) • Water – Reflectance regularly decreases from visible to NIR – Complete absorption in NIR – When the water is loaded with particles, the curve shows a similar form but the reflectance is higher.

EM Radiation – Object Interactions

EM Radiation – Object Interactions

Aerial Photography • • First Method of Remote Sensing Low altitude analog/ digital pictures High information content Important as historical documents

Important Components of an Aerial Photograph Clock Level Principle point – photo center Altimeter Camera constant Fiducial marks

• Comparison of Aerial Photographs with Maps Air Photos

Flight planning • Aerial photographs are normally taken with 60 -80% overlap and 20 -30% sidelap

Vertical Aerial Photography d Film Plane Principal point Focal length – Camera constant Optical axis Projection center Flying height Ground D

Vertical Aerial Photography • Terminology – Center of Projection • All rays of light reflected from the ground must pass this point – Optical Axis • The line through the projection center, perpendicular to the film plane. This shows the photo direction – Principal Point • Point where the optical axis hits the film plane. The approximate principal point is the photo center – Focal Length • The distance between the principal point and the center of projection. – * Camera constant

Scale Calculations in Aerial Photography Scale of a map Relative distance between two points on the map compared to the true horizontal distance between the same points in the terrain. This relation is called the representative fraction – 1: S or 1/S S = Scale Factor

d c 1/s = d/D = c/H S = D/d = H/c H D

Practical Procedure for Scale Correction • Identify two points in the air photos, situated on level ground • Measure the distance between two points in the field (D) • If maps are available, use them to find D • In individual photos, indicate the center point of each photo. For measurements, always choose the photo where the area of interest is as close as possible to the photo center • Measure the photo distance between the points selected (d) • The Scale Factor (S) – S = D/d

• Examples • Aerial photographs have no definite scale.

• A photo survey has been carried out at a height of 4560 m above the mean altitude of the area. The camera used has a focal length of 152. 00 mm. – What is the mean scale of the photo? – What is the scale at a hilltop situated approximately 380 m above the mean altitude of the terrain? – What is the scale at a valley floor approximately 228 m below the mean altitude of the terrain?

Focal length of camera is 150 mm Flying height is 3000 m above the mean altitude A 2750 msl B 2450 msl Mean Altitude 1850 msl C

Applications of Aerial Photography • • • Land use mapping Soil mapping Geological applications Soil erosion and landslide studies Topographical analysis Urban planning

Aerial Photography – play an important role in the execution of cartographic mapping on various scales and in evaluation of natural resources of a region. – involves qualitative examination of the terrain, the correct correlation of the observed data and finally the quantitative evaluation of data. – offers possibility of detailed study of the terrain – full use of immense wealth of information recorded on an aerial photograph, which not only economize and expedite the investigation but offer more reliable results.

Satellite Remote Sensing • • Acquire images from space Earth observation satellites – earth surface monitoring Weather satellites – meteorological applications Digital multi-spectral information – easy to interpret using computers Earth Observation Satellites Landsat SPOT IRS IKONOS NOAA ASTOR

Satellites and their Sensor Properties • Satellite Orbits – Geostationary & Polar Orbiting

Satellites and their Sensor Properties • Spatial Resolution – The area covered by a single pixel on the ground (Pixel is the smallest homogenous area of a recorded image) – Small pixels – High spatial Resolution – Large pixels – Low spatial resolution • Spectral Resolution – Spectral resolution describes the ability of a sensor to define wavelength intervals. • Temporal Resolution – Frequency of obtaining data over a given area • Radiometric Resolution – The radiometric resolution of an imaging system describes its ability to discriminate very slight differences in energy.

Scale Diversity of Remote Sensing Data Global to Local NOAA AVHRR OCM Wi. FS LISS-III PAN IKONOS