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

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

1 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Yrd. Doç. Dr. Ali DENİZ

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

3 Introduction to Remote Sensing 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;

4 Introduction to Remote Sensing 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 Kirckhoffs law; Since the emitted radiance is a function of distribution of objects, measurements of radiance gives information about them.

5 Introduction to Remote Sensing 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/m 2 sr cm -1 (...)

6 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 is a solid angle and is defined as: d d (...)

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

8 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 When a monochromatic radition in Figure- whose radiance is L 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. (...)

9 Introduction to Remote Sensing 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.

10 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Black Body Radiation: 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.

11 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 The ratio of emitted radiance by an object to the radiance emitted by a blackbody at the same temperature is called emisivity ( ). = 1 for blackbody. < 1 for greybody. Blackbody radiation Greybody radiation E

12 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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: Where h is Planck const, k is Boltzmann const. (...)

13 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Figure-... Spectral Radiance of Blackbody Kelvin

14 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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)= E 4 Where is stefan Boltzmann constant. (...)

15 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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. max =0.2897/T (cm) E What wavelengthg gives maximum energy

16 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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 0.50 m which is the center of the visible region of te spectrum. On the other hand eaths atmospheric temperature is about 255 K. Maximun emitted energy takes place around 11 m which is infrared region (Figure...).

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

18 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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=E rot +E vib +E elc +E trans

19 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Absorption or emmision occurs when molecule changes from energy level E 1 to E 2 with a frequency f = (E 1 - E 2 ) / h. Where h is a planck constant. 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. Significance in the spectrum:

20 Introduction to Remote Sensing 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, N 2 O, H 2 O and O 3 have dipole moments while N 2, O 2, CO 2 and CH 4 do not. However, as CO 2, and CH 4 vibrate electrical dipole moment is produced and so rotational interaction take place. Therefore, vibration-rotation interaction takes place with the incident wave.

21 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 O-C-O O-CO Symetric Stretching Bending Asymetric Stretching Figure-... Vibration modes of CO 2 =7.46 m =14.98 m =4.26 m (Wavelength of vibration) No static and dynamic electric dipole So no interection with the incident radiation So no absoption (Figure-...). Dipole occurs due to bending Vibration (vibration-rotation) so Absoption takes place (Figure-...).

22 Introduction to Remote Sensing 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 CO 2 bands are used for temperature soundings. The 6.3 m H 2 O band is used for water vopour. The 9.6 m O 3 band is used for the total ozone measurements.

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

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

25 Introduction to Remote Sensing 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-...).

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

27 Introduction to Remote Sensing 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).

28 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Radiative Transfer Equation (RTE): 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. (...)

29 Introduction to Remote Sensing 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. (...)

30 Introduction to Remote Sensing 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.

31 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Figure-... NOAA HIRS weighting functions.

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

33 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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... Brain Storming!

34 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Processes of Atmospheric Radiation: Land Ocean emitted transmitted reflected absorbed, emitted and scattered by aerosols and molecules absorbed emitted reflected absorbedtransmitted emitted transmitted reflected transmitted absorbed &scattered Figure-... Process of Atmospheric Radiation

35 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Sensors: 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.

36 Introduction to Remote Sensing 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. Negatively Charged Plate Photon beam R C C Figure-... Shemetic view of a detector.

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

38 Introduction to Remote Sensing 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).

39 Introduction to Remote Sensing 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.

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

41 Introduction to Remote Sensing 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.

42 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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.

43 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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. Temperature Sounding Retrieval:

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

45 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Assuming linearity and introducing basis function by matrix inversion; 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 ofgives the solution as: b=A -1 R Σ(R-Σab) 2 (...) b=(A T.A) -1.A T.R (...)

46 Introduction to Remote Sensing 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)

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

48 Introduction to Remote Sensing 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 (V H-1/2 + V H+1/2 ) Wind direction is the vectorial sum of two winds: V H-1/2 V H+1/2 V

49 Introduction to Remote Sensing 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.

50 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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.

51 Introduction to Remote Sensing 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 L cd = L bcd +(1- )L cl where L bcd is radiance from completely opaque cloud. After expresing L cl and L bcd in the form of RTE and some algebric manipulation, it becomes: (…)

52 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Where is called effective cloud amount. L cl 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: (…)

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

54 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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.

55 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Histogram: 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.

56 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September VIS IR Cloud id VIS count IR Count High clouds Cirrus thin Medium clouds Low clouds Warm land Sea Figure_... Bi-dimentional histogram of IR vs VIS Kernels of the classes are:

57 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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).

58 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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 (T 11 -T 12 ) (…) Where T in K and SST in Celsius.

59 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 At nightime SST is given by: SST 1 =1.0088T (T 3.7 -T 11 ) SST 2 =1.0350T (T 11 -T 12 ) SST 3 =1.0170T (T 3.7 -T 12 ) All three SST result must agree within 1K to be accepted. (…)

60 Introduction to Remote Sensing 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

61 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 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, (…)

62 Introduction to Remote Sensing 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.

63 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Calibration: 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.

64 Introduction to Remote Sensing 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:

65 Introduction to Remote Sensing WMO-RMTC-EUMETSAT Satellite Meteorology Course, Alanya, Turkey September 2003 Orbits: The motion of the satellites around the earth is governed by the Newtons law of motion. satellite r earth Satellite orbit The attractive force is:

66 Introduction to Remote Sensing 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 spacecrafts 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.

67 Introduction to Remote Sensing 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 Keplers 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.

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

69 Introduction to Remote Sensing 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. 850 km). Geostationary orbit consides with the earths 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.


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