Remote Sensing Waves transport energy Remote Sensing According

Remote Sensing Waves transport energy

Remote Sensing • According to quantum theory, light may be considered not only as an electro-magnetic wave but also as a "stream" of particles called photons which travel at speed c, the vacuum speed of light. • Each particle carries one quantum of energy Q = hf where: h is Planck's constant f is the frequency of the light • Short wavelenghts high energy • Long wavelenghts low energy

Remote Sensing 4μm 7μm

Remote Sensing

Remote Sensing • Any object above 0 K (-273°C) emits electromagnetic energy • How much is given by the law of Stefan-Boltzmann M = ε σ T 4 where: σ is a constant ε is the emissivity coefficient • For a blackbody, ε is = 1. A blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. A blackbody in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black body radiation.

Remote Sensing The wavelength at which a black body radiation curve reaches a maximum is given by the Wien’s wavelength displacement law λmax = A / T where A = ~2898 μm K

Remote Sensing

Remote Sensing

Remote Sensing Scattering occurs when particles or large gas molecules present in the atmosphere interact with and cause the electromagnetic radiation to be redirected from its original path. 3 types of scattering: Rayleigh scattering occurs when particles are very small compared to the wavelength of the radiation. Rayleigh scattering causes shorter wavelengths of energy to be scattered much more than longer wavelengths sky is blue Mie scattering occurs when the particles are just about the same size as the wavelength of the radiation. Water vapour is a common causes of Mie scattering clouds are white Non selective scattering this occurs when the particles are much larger than the wavelength of the radiation. Water droplets and large dust particles can cause this type of scattering haze and smog

Remote Sensing Absorption causes molecules in the atmosphere to absorb energy at various wavelengths. Ozone Absorbs the harmful (to most living things) ultraviolet radiation from the sun. Without this protective layer in the atmosphere our skin would burn when exposed to sunlight. Carbon dioxide Absorbs radiation strongly in the far infrared portion of the spectrum - the area associated with thermal heating - which serves to trap this heat inside the atmosphere. Water vapour Absorbs much of the incoming longwave infrared and shortwave microwave radiation. The presence of water vapour in the lower atmosphere varies greatly from location to location and at different times of the year

Remote Sensing

Remote Sensing Et + Er + Es + Ea = Einc

Remote Sensing Radiance vs. Reflectance • Radiance is the variable directly measured by remote sensing instruments. Radiance most often has units of watt/(steradian/square meter). • Reflectance is the ratio of the amount of light leaving a target to the amount of light striking the target. It has no units. • Reflectance is a property of the material being observed. • Radiance depends on the illumination (both its intensity and direction), the orientation and position of the target and the path of the light through the atmophere. • With effort, many of the atmospheric effects and the solar illumination can be compensated for in remote sensing data. This yields something which is called "apparent reflectance" and it differs from true reflectance in that shadows and directional effects on reflectance have not been dealt with. • For many applications, radiance and apparent reflectance can be used interchangibly. However, since reflectance is a property of the target material itself, you will get the most reliable results using reflectance.

Remote Sensing specular diffuse

Remote Sensing clean water turbid water

Remote Sensing

Remote Sensing

Remote Sensing

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Remote Sensing

Remote Sensing Resolutions • Spectral: refers to the width of spectral bands. • Radiometric: sensitivity to differences in the power of the incoming radiation. • Geometric: minimum distance between objects perceived as separated (distinguishable detail) • Temporal: period of time between two acquisition over the same area.

Remote Sensing

Remote Sensing

Remote Sensing 8 bits 3 bits 4 bits 2 bits

Remote Sensing 10 m 40 m 20 m 80 m

Remote Sensing

Remote Sensing

• • Li. DAR stands for Light Detection and Ranging, commonly known as Laser Radar Each time the laser is pulsed: – Laser generates an optical pulse – Pulse is reflected off an object and returns to the system receiver – High-speed counter measures the time of flight from the start pulse to the return pulse – Time measurement is converted to a distance (the distance to the target and the position of the airplane is then used to determine the elevation and location) – Multiple returns can be measured for each pulse

Remote Sensing

Remote Sensing • High spatial resolution – Laser footprint on ground ≤ 0. 50 meters – Typical density is 0. 5 to 20+ pulses/m 2 – 2 to 3 returns/pulse in forest areas • Large volume of data – 5, 000 to 60, 000+ pulses/hectare – 10, 000 to 100, 000+ returns/hectare – 0. 4 to 5. 4+ MB/hectare • Raw return data is a cloud of XYZ points

Remote Sensing

Remote Sensing

Remote Sensing

Remote Sensing

Remote Sensing Streams

Remote Sensing

Remote Sensing

Remote Sensing

Remote Sensing Natural colours 3 0. 65µm VIS 2 0. 55µm VIS 1 0. 48µm VIS 3 0. 85µm NIR 3 R 2 G 1 B 2 0. 65µm VIS 1 0. 55µm VIS False colours

Remote Sensing Water Forest Urban area Fields

Remote Sensing Enhancement • Whenever satellite images are visualized using the direct correspondence between the digital values of pixels and the intensity levels of primary colors on screen, they appear to be dark and poorly contrasted. • Indeed, generally the digital values associated to the pixels do not cover the entire range of useable digital values. The sensibility of the sensor is tuned to avoid out-of-scale measurements, even when scanning over lowly or highly reflective surfaces. • A typical image histogram shows a peak of slightly scattered, low values.

Remote Sensing Enhancement • Contrast stretching is an expansion of the intensity levels used in visualizing the image to the entire range of usable intensity levels, by means of a linear or non-linear transformation. • This is obtained using the so called Lookup Tables (LUT), an array of pairs of values that map the input values to the output levels of the display. • The images very often contain a few very high values (clouds, small-highly-reflective surfaces, sensor errors), as well as few very dark values (shadows, non-reflective surfaces, sensor errors), thus generally the “tails” of the histogram that may contain anomalous values are not taken into account when building the stretch LUT.

Remote Sensing Enhancement 255 pixel count 0 255 0 INPUT OUTPUT . . . 120 160 121 163 122 166 123 169 124 172 125 175 126 178 127 181 128 184 129 187 130 190 131 193 132 196 133 199 134 202 135 205 136 208 137 211 138 214 . . .

Remote Sensing Enhancement

Remote Sensing Enhancement

Remote Sensing Enhancement