# Yrd. Doç. Dr. Ali DENİZ WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey 22-25 September 2003.

## Presentation on theme: "Yrd. Doç. Dr. Ali DENİZ WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey 22-25 September 2003."— Presentation transcript:

Yrd. Doç. Dr. Ali DENİZ WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

What is remote sensing? Remote sensing is defined as the way to infer about the objects from distance i.e size, consentration, content etc. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

The interaction of electromagnatic waves with the objects
modifies the incident wave; The resulting sinature depands on the composition and structure of the medium; The principle of measurements of the Atmospheric parameters i.e. temperature and humidity is the interpretation of measured radiation in the specific spectral intervals which are sensitive to the constituent; WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

In the infrared and microwave regions of the spectrum
atmospheric constituents absorbs the radiation; then emit According to Kirckhoff’s law; Since the emitted radiance is a function of distribution of objects, measurements of radiance gives information about them. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Absorption and Transmission of Monochromatic (spectral) Radiation:
The amount of energy, radiance, crossing a differencial area dA in a time integral dt and wavenumber v is given as: (...) L= dE / Cos dA dt d d its unit is W/m2 sr cm-1 WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

is a solid angle and is defined as:
(...) d d WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Absorption: L Incident beam Figure-.. Absorption through a Medium
Attenuated exit beam Absorbing medium X L dx Incident beam Figure-.. Absorption through a Medium WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

peneterates into absorbing medium (non scatering) the fractional decrease is: d L/ L = -k  dx (...) Where  is the density of medium, k is the spectral absoption Coefficient. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

When integrating equation ... between 0 and x, becomes:
(...) Where L(0) is the radiance entering the medium at x=0, is called optical depth. And is called transmittance. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Blackbody radiation field is characterised as:
Isotropic and nonpolarized; Independent of shape of cavity; Depends on only temperature (T). In a perfect blackbody emisivity is equal to unity due to thermodynamic equilibirium. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

emitted by a blackbody at the same temperature is called emisivity (). Blackbody radiation E  = 1 for blackbody.  < 1 for greybody. Greybody radiation WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

To explain the spectral distribution of radiance emitted
Planck Law: To explain the spectral distribution of radiance emitted by solid bodies, Planck found that the radiance per unit frequency emitted by a blackbody at temperature (T) is given as: Planck function Where h is Planck const, k is Boltzmann const. (...) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Kelvin Figure-... Spectral Radiance of Blackbody WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

It gives the total radiation of a cavity (blackbody) not spectral
Stefan Boltzmann Law: It gives the total radiation of a cavity (blackbody) not spectral distribution of radiation. When Planck function (...) is integrated 0(zero) to infinity (), S-B is given as: E(Exitance)=E4 Where  is stefan Boltzmann constant. (...) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

When Planck equation is differentiated w.r.t wavenumber
Wien Law: When Planck equation is differentiated w.r.t wavenumber () or wavelength () and equated to 0(zero), one can find max for a given temperature (T) called Wien Law. What wavelengthg gives maximum energy E max =0.2897/T (cm) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

On the other hand eath’s atmospheric temperature is about 255
The radiative temperature of the sun surface is about 5780 K. After applying Wien law, maximum Planck radiance is obtained at the wavelength (max ) of m which is the center of the visible region of te spectrum. On the other hand eath’s atmospheric temperature is about 255 K. Maximun emitted energy takes place around 11 m which is infrared region (Figure...). WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Brightness Temperature (or equivalent blackbody temperature) is the temperature estimated by inverting Planck function. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

In the atmosphere, the absorption of radiation is mostly due to gases.
Gaseous Absorption: In the atmosphere, the absorption of radiation is mostly due to gases. Major interest for the transfer of radiant energy is the value of absorption coefficient (spectroscopy). Total energy of a molecule consists of rotation, vibration, electronic, and translation. E=Erot+Evib+Eelc+Etrans WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Absorption or emmision occurs when molecule changes
from energy level E1 to E2 with a frequency f = (E1- E2 ) / h. Where h is a planck constant. Significance in the spectrum: rotational energy in the microwave and far IR regions; vibrational energy in the near IR region; electronic as well as vibrational and rotational energy in the visible and UV regions. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

In order to posses rotational energy (interact with
the elecrtromagnatic field), molecules shall have dipole moment. Atmospheric such gases important for satellite meteorology as CO, N2O, H2O and O3 have dipole moments while N2, O2 , CO2 and CH4 do not. However, as CO2, and CH4 vibrate electrical dipole moment is produced and so rotational interaction take place. Therefore, vibration-rotation interaction takes place with the incident wave. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

O-C-O O-C-O O-C O =7.46 m =14.98 m =4.26 m
No static and dynamic electric dipole So no interection with the incident radiation So no absoption (Figure-...). (Wavelength of vibration) Symetric Stretching Dipole occurs due to bending Vibration (vibration-rotation) so Absoption takes place (Figure-...). O-C-O =14.98 m Bending O-C O =4.26 m Asymetric Stretching Figure-... Vibration modes of CO2 WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Temperature Sounding and measurements of some trace gases
in the atmosphere are based on vibrational transition. For example; The 15 m and 4.3m of CO2 bands are used for temperature soundings. The 6.3 m H2O band is used for water vopour. The 9.6 m O3 band is used for the total ozone measurements. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Figure-... IR transmittance of several gases in the atmosphere (after Kidder,S.Q)
WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Radiation scattered from a particle depends on: Size; Shape;
Scattering: Radiation scattered from a particle depends on: Size; Shape; Index of refraction; Wavelength of radiation; View geometry. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Fundemental two types of scattering are Mie and Rayleight.
For Rayleight scattering,  >>  For Mie scattering,  ≈  Where  is particle size. Scattering properties of such aerosols as smoke, dust, haze in the visible part of the spectrum and of cloud droplets in the IR region can be explanined by Mie scattering, while of air molecules in the visible part can be explained by Rayleight Scattering (Figure-...). WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Figure-... Scattering Properites of atmospferic Contitiuens (after Kidder, S.Q).
WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Scattering phase function determines the direction in which
the radiation is scattered. As the size parameter (x=2πr/) inreases, more scattering takes place in the forward direction (Figure-...). Figure-...Scattering phase function of water droplets (after Kidder, S.Q). WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Consider a volume of gas (Figure-...) where absorption and emission takes place but no scattering, energy transfer equation can be written as: (...) Where first therm on the right hand side is abrorption within dx and second term is emission within dx. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Applying Kirchhof law and some manpulation and integration
finally we get: (...) The first term on the right hand side is the radiance at the Boundary multiplied by the transmitance from the boundary to a. Second term is the contribution due to emission from the medium in the direction of incident wave. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Similar equation can be computed for the emitted radiance
in the atmospfere with  zenith angle as: (...) where and is called weighting function. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Figure-... NOAA HIRS weighting functions.
WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

So equation (...) can be written in a more compact form as:
Radiance at the TOA Surface contribution Atm layer cont. z TOA , B(T) dz τ L(0)=εs,ν B(T) surface WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Previous RTE (Figure-...) is driven in cartesian coordinate system
Brain Storming! Previous RTE (Figure-...) is driven in cartesian coordinate system drive it in presure coordinate system in p by using hydrostatic Equation. Where q is mixing ratio and g is gravity. Good luck... WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

transmitted absorbed, emitted and scattered by aerosols and molecules reflected absorbed &scattered emitted transmitted transmitted reflected emitted reflected emitted Land transmitted absorbed absorbed Ocean Figure-... Process of Atmospheric Radiation WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Sensors are the devices for detecting the photons. The critical
part of the sensors is the detectors which works based on photoelectric effect. That is, There will be an emmision of negative particles (electrons) when negatively charged plate is subject to a beam of photons. The electrons then can be made to follow,collected and counted as signals. The magnitude of electric current (number of photoelectrons per unit volume is directly proportional to light intensity. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Thus, the change of electric current can be used to measure
the change in the photons (number, intensity) which strikes the plate during the given time interval. Photon beam C Negatively Charged Plate R C Figure-... Shemetic view of a detector. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Remote Sensor Types: passive Sensor types aktive non-imaging imaging
Microwave radiometer Magnatic ensor Gravimeter Fourier spectrum non-imaging non-scaning passive Monochrom IR imaging Camera TV camera imaging image plane scanning Solid scanner Sensor types scanning Optical mechanical scan. object plane scanning Microwave radiometer non-scaning non-imaging Microwave radiometer Microwave altimeter aktive image plane scanning Passive phased array radar scanning imaging Real aperture radar object plane scanning Synthetic aperture radar WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Passive sensors: Radiation comes from the external sources.
Active sensors: Radiation is generated within the sensor. Non-imaging: Measured radiation received from all points in the sensed target and integrated. Imaging: Radiaiton is received from a specific points (pixels) in the target end result is an image(picture). Sensors which instantaneously measure radiation coming from entire scene called framing systems e.g eye, camera; if the scene is sensed point by point along successive lines over finite time called scanning systems. The size of scene which is determined by the aperture and optics called field of view (FOV). WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Radiometer is the general term for any instrument which
quantitatively measures the EM radiation in some interval of EM spectrum. When the radiation is light from the narrow visible band, the term photometer is used. If the sensor includes such components as prism or difraction grating which can break incoming radiation into discrete wavelengths and despers them to detectors called spectrometer. Spectroradiometer implies that dispersed radiation is in bands (Δλ) rather than discrete wavelenght (); most space sensors are of this type. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Retrieval methods can be classified in three general categories:
Physical; Statistical and; Hybrid. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

To predict the obserable parameters from arbitrary model
parameters called forward problem; on the other hand, invers problem is to infer the model from observed parameters, Invers problems are “ill posed”; that is, the solution is not unique. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Estimation of L(z) from known temperature profıle, T,
Example: Estimation of L(z) from known temperature profıle, T, is a forward problem, while estimation of T profile from satellite measurement of L(z) is an invers problem. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Temperature Sounding Retrieval:
Physical Retrieval: It is based on itiration of RTE by using first guess NWP profile until the desired solution is optained. Statistical Retrievals: The siplest is to make regression between radiosonde sounding called training data and measured radiance. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

RTE can be written in the dicrete formas:
Hybrid Retrieval: RTE can be written in the dicrete formas: After putting surface contribution into Summation and replacing Li by Ri. in maxrix notation Where W is a matrix containing discrete weighting function. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Assuming linearity and introducing basis function
by matrix inversion; b=A-1R (...) Which is an exact solution of RTE. However not a satisfactory solution because it is ill conditioned; smaller error in R results in larger errors in B. Trying least square fit of Σ(R-Σab)2 gives the solution as: b=(AT.A)-1.AT.R (...) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Which is better solution than equation (...), yet it can be
improved by applying other methods (e.g. minimum variance) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Atmospheric wind retrieval from the images is based on
cross correlation method of successive three images. cc pick center of search area Wind wector VH+1/2 VH-1/2 cc pick 32x32 pixel H 96x96 96x96 Image 2 (target image) Image 1 (H-1/2) Image 3 (H+1/2) First, cross-correlation matrix produced between target image and Last image (H+1/2) to find the correlation peak . WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

The distance between the center of search and the cc peak
is the cloud tracking wind vector. In order to eleminate the spurious (false) peak cc is estimated between the target image and first image (H-1/2). If cc peaks are not symetric, it is rejected. If not, wind speed is claculated as: V=1/2 (VH-1/2 + VH+1/2 ) Wind direction is the vectorial sum of two winds: VH-1/2 V VH+1/2 WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Height assignment: After finding the most contributing cloud
cluster to cc peak, its top temperature is used to assign height to V by means of NWP forecast temperature profile. CO2 slicing method can also be used for height assignment gives better solution. Sea surface wind speed and direction are estimated by means of scatterometer which works like a radar. Tracking winds can also be retrieved from atmospheric soundings data. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Radiance measurements around 15m CO2 band ( e.g HIRS
CO2 Slicing: Radiance measurements around 15m CO2 band ( e.g HIRS sounder) allows to detect clouds at various level. In the center of band, upper level clouds and at the wings lower level clouds are detected (Figure …). Cloud amont and level (top pressure) can be estimated by means of RTE. Effectively detects thin cirrus clouds which are missed by IR window and VIS channels. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Radiance from the partly cloudy regions are given by
L=Lcd+(1-)Lcl where  is a fractional cloud cover, Lcd is radiance from clouds and Lcl is radiance from clear air. The cloud radiance is given by Lcd=Lbcd+(1-)Lcl where Lbcd is radiance from completely opaque cloud. After expresing Lcl and Lbcd in the form of RTE and some algebric manipulation, it becomes: (…) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Where  is called effective cloud amount. Lcl estimated from
known temp and moisture profiles and L is a satellite measurement (e.g HIRS). Right hand side is calculated from known temp profile and atmospheric transmitance profile. Representing left hand side with, L, and right hand side, B, and taking the ratio of two spectral channels which see the same FOV (e.g 14.2m/14.0m or 14.2m/13.3m), it becomes: (…) WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

The optimum cloud pressure is obtained when the absolute
differences of right hand side and left hand side is minimum. Once the cloud height is determined, an effective cloud amount can be estimated by using IR window channel. Sat measurement. (…) Calculated from temp profile Opaque cloud radiance. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Objective cloud retrieval is carried out by using imaging
Clouds: Objective cloud retrieval is carried out by using imaging radiometers rather than sounders due to their high resolution. Widely used cloud analysis techniques are: Threshold: Temperature thresh is set for the spectral channels such that if pixel temp is colder, it is assigned as a cloudy pixel. Level of the cloud is determined by comparing brightness temp of pixel with a known temp sounding. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

It is based on the histogram analysis of pixels which
represent cloud types and surface. Various dimentional histograms may be constructed. Figure-… shows two Dimentional ( IR vs VIS) historam analysis.High clouds are located on the cold region while middle clouds are clustered at the center and sea pixels are clustered warm (dark) region. Histogram WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Kernels of the classes are:
230 Cloud id VIS count IR Count 220 High clouds Cirrus thin Medium clouds Low clouds Warm land Sea 200 IR 180 150 130 VIS Figure_... Bi-dimentional histogram of IR vs VIS WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

For an area of pixels, standard deviations (SD) and mean
Pattern recognition: For an area of pixels, standard deviations (SD) and mean values are Calculated. Uniform scenes (cloudy or clear) tend to have low standard deviation while partly cloudy scene tends to have high standard deviation. Estimated statistical values (SD and mean etc) compared with the background information (e.g. Climatological) to classify the scene (cloudy, land, sea). WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

For the scene classified as sea, after applying atmospheric
SST: For the scene classified as sea, after applying atmospheric correction, the radiance is converted to brightness temperature by means of Planck function. For NOAA, SST estimation is based on the reression Between Brightness temperatures of the channels (11 m, 12 m and 3.7 m) ans SST. For sea scene, in the daytime SST is: (…) SST=1.9346T (T11-T12) Where T in K and SST in Celsius. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

At nightime SST is given by:
SST1 =1.0088T (T3.7-T11) SST2 =1.0350T (T11-T12) SST3 =1.0170T (T3.7-T12) (…) All three SST result must agree within 1K to be accepted. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Split Window Technique:
Making of two measurements rather then one in the atm window region (near 11 m ) called split window. The two channel see the same absorbers but in different amount. The aim of the split window is to correct atm attenuation (mostly due to water vapour) to estimate better surface temperature. The siplit window equation driven as follows: in the windows region transmitance can be expressed as  = exp(-ku), using talor expention, = 1-ku and d=-kdu then RTE becomes WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Where B is mean atm radiance and u total atm absorbtion
(…) Where B is mean atm radiance and u total atm absorbtion path length due to water vapour. After linearizing the RTE and using for two channels (e.g. 11 and 12 m ), we get (…) Where Ts is a surface skin temp corrected for water vapour, WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

k is absorption coefficient and T 1 and T 2 are brightness
temp for the windows channels. In a similar manner atm precipitable water can be retrieved. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Calibration is the process to obtain physical parameters
(e.g. Tempareture) from the radiometric measurements (count) On board Calibartion: Hot and cold targets located in the spectrometer are sensed to get relative radiomatric responses to estimate calibration slope. Vicarious calibration: The method of vicarious calibration by means of calculated radiance allow absolute calibartion of radiometers. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

It works by comparing radiometric count to be calibrated
with corresponding alsolute radiance which is calculated from actual atmospheric parameters (e.g. Temperature and humidity profile). Radiometric respons to the radiance can be linear or nonlinear. In the case of linear response (e.g. METEOSAT) calibration coefficient is calculated as: WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

The motion of the satellites around the earth is governed
Orbits: The motion of the satellites around the earth is governed by the Newton’s law of motion. The attractive force is: r satellite earth Satellite orbit WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Where M is earth mass, m is satellite mass, and g is garvitational
Constant.The centrifugal force of the spacecraft’s motion in orbit must balance the attraction force such that: introducing period T=2r/v and substituting in the equation we get: Ex: NOAA satellites are app 850 km above the earth surface, inserting into equation T=102 min. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

However, real satellite orbit is nerly elliptical due to
the external foreces(e.g. gravitational potential of earth, solar pressure). Eliptical orbit is to be explained by Kepler’s law. Six orbital elements are used to express the spacecraft position given by: Semimajor axis,a (km); Eccentricity,e; Inclination,i (degree); Right ascensing of ascending node,  (degree); Argument of perigee,  (degree); And true anomaly, , degree. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

For the meteorological satellites, mainly two orbits are used:
Z spacecraft Orbit plane apogee earth perigee Y a i Equator plane X Ascending node Ascending node For the meteorological satellites, mainly two orbits are used: and sunsynchronous and geostationary. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

Sunsynchronous orbit have high inclination angle (e.g
98.7 for NOAA sat), pass the equator at the same local time, and located in the lower orbit (e.g km). Geostationary orbit consides with the earth’s equatorial plane, located nearly 36 km above the equator. Geostationary satellites drift from the desired orbit so that periodic orbit manoeuvres are needed in the east-west and north-south directions and vise versa. WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003

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