Introduction to Remote Sensing

Guido Cervone

Remote Sensing

Remote Sensing is the technology that is now the principal modus operandi (tool) by which the Earth's surface and atmosphere, the planets, and the entire Universe are being observed, measured, and interpreted from such vantage points as the terrestrial surface, earth-orbit, and outer space.

More generally: Acquire data without being in contact with it

Examples of Remote Sensing Data

Examples of Remote Sensing Data

Examples of Remote Sensing Data

Early Applications of Remote Sensing

At the beginning of the 20th century a Bavarian pigeon fleet that operated in Europe.

Early Applications of Remote Sensing

In 1906 an ingenious effort by "flying" cameras on kites to study the damage in San Francisco, right after the catastrophic earthquake

Here is the resulting composite photo

Early Applications of Remote Sensing

Remote Sensing became a reliable instrument as humans learned how to fly

Early Applications of Remote Sensing

The logical entry of remote sensors into space on a routine basis began with automated photo-camera systems mounted on captured German V-2 rockets, launched out of White Sands, NM

These rockets also carried geophysical instruments in their nose cones, which were returned to Earth by parachute

Early Applications of Remote Sensing

The modern Space program is held by many historians to truly have begun with the launch of Sputnik I by the Soviets on October 4, 1957

Today’s Remote Sensing

Remote sensing technology is very advanced We can observe the Earth and its environment

with a large array of instruments with very high spatial, spectral and temporal resolution

Such observations give us unprecedented access to massive amount of data

Space Countries

Since the 1950s several countries have been sending satellites into space

At first, the USA and the Soviet Union were the only countries capable of launching satellites into orbit

Nowadays many countries have capabilities to launch satellites into orbit

Satellites use was primarily military Reconnaissance Communication

Space Countries

Nowadays several countries can independently send satellites into space

Applications are both Military and Civilian Reconnaissance Communication Navigation What else?

Space Countries

Earth’s Gravitational Pull

• The Earth's gravity pulls everything toward the Earth. In order to orbit the Earth, the velocity of a body must be great enough to overcome the downward force of gravity

One important fact to remember is that orbits within the Earth's atmosphere do not really exist. Atmospheric friction caused by the molecules of air (causing a frictional heating effect) will slow any object that could try to attain orbital velocity within the atmosphere.

In space, with virtually no atmosphere to cause friction satellites can travel at velocities strong enough to counteract the downward pull of Earth's gravity

The satellite is said to orbit around the Earth

Orbits

Orbit refers to the path of a smaller object (secondary) around a bigger object (primary) as a result of the combined effects of inertia and gravity.

Satellite Orbit

One of the most important aspect of a satellite orbit is its inclination

The inclination limits the types of coverage and data that a satellite can acquire

The velocity of the satellites determines the height above the geoid

Satellites Orbit

Geosyncronous Satellites

GEO are circular orbits around the Earth having a period of 24 hours. A geosynchronous orbit with an inclination of zero degrees is called a

geostationary orbit. A spacecraft in a geostationary orbit appears to hang motionless above

one position on the Earth's equator. For this reason, they are ideal for some types of communication and meteorological satellites.

A spacecraft in an inclined geosynchronous orbit will appear to follow a regular figure-8 pattern in the sky once every orbit.

To attain geosynchronous orbit, a spacecraft is first launched into an elliptical orbit with an apogee of 35,786 km (22,236 miles) called a geosynchronous transfer orbit (GTO). The orbit is then circularized by firing the spacecraft's engine at apogee.

Typical Geostationary Coverage

Metereological Satellites

World Clouds

Polar Orbits

PO are orbits with an inclination of 90 degrees.

Polar orbits are useful for satellites that carry out mapping and/or surveillance operations because as the planet rotates the spacecraft has access to virtually every point on the planet's surface

Most PO are circular to slightly elliptical at distances ranging from 700 to 1700 km (435 - 1056 mi) from the geoid.

At different altitudes they travel at different speeds.

(Near) Polar Orbiting Satellites

Ascending Vs. Descending

Daily Coverage

Polar Regions

The satellite doesn't pass directly over the pole due to the slight inclination of the orbital plane.

The transparent overlay identifies the 3000 km wide swath that is viewed by the AVHRR imaging instrument on the satellite.

The yellow curves delineate the limits of the 60 degree viewing arcs from the six "standard" geostationary satellites included in these discussions.

Sun Synchronous Orbits

SSO are near polar orbits where a satellite crosses periapsis at about the same local time every orbit.

This is useful if a satellite is carrying instruments which depend on a certain angle of solar illumination on the planet's surface.

In order to maintain an exact synchronous timing, it may be necessary to conduct occasional propulsive maneuvers to adjust the orbit.

Most research satellites are in Sun Syncronous Orbits

There is a special kind of sun-synchronous orbit called a dawn-to-dusk orbit. In a dawn-to-dusk orbit, the satellite trails the Earth's shadow (Why do you think this could be convinient?)

Molniya Orbits

They are highly eccentric Earth orbits with periods of approximately 12 hours (2 revolutions per day).

The orbital inclination is chosen so the rate of change of perigee is zero, thus both apogee and perigee can be maintained over fixed latitudes.

This condition occurs at inclinations of 63.4 degrees and 116.6 degrees. For these orbits the argument of perigee is typically placed in the southern hemisphere, so the satellite remains above the northern hemisphere near apogee for approximately 11 hours per orbit. This orientation can provide good ground coverage at high northern latitudes.

Molniya Orbits

Tundra Orbits

Tundra orbit is a class of a highly elliptic orbit with inclination of 63.4° and orbital period of one sidereal day (almost 24 hours).

A satellite placed in this orbit spends most of its time over a designated area of the earth, a phenomenon known as apogee dwell.

Different Orbital Distances

Satellite Constellation

A group of electronic satellites working in concert is known as a satellite constellation.

Such a constellation can be considered to be a number of satellites with coordinated ground coverage, operating together under shared control, synchronised so that they overlap well in coverage and complement rather than interfere with other satellites' coverage.

Satellite Formation

Remote Sensing and Aviation

How can we use the data from past, current and future satellite missions? Atmospheric chemistry Cloud physics Turbulence Volcanic Ash Mesoscale modeling Transport and Dispersion modeling