spectrogram

7/28/2019 Spectrogram

http://slidepdf.com/reader/full/spectrogram 1/21



GoalsO Definition & application of

SPECTROGRAM and MULTIPATH

O How to build SPECTROGRAMO Characteristic of MULTIPATH

O How to simulate all of them using

MATLAB



spectrum spectrogram



O The horizontal axis represents time.

O The vertical axis is frequency

O A third dimension indicating the amplitude of a particular

frequency at a particular time is represented by the

intensity or colour of each point in the image.



Short time fourier transform



Window size’s effection O A wide window gives better frequency

resolution but poor time resolution.

O A narrower window gives good timeresolution but poor frequency resolution.

These are called narrowband and

wideband transforms, respectively.



Build spectrogram



SpectrogramsO Spectrograms can be used to identify

spoken words phonetically , and to

analyse the various calls of animals.O They are used extensively in the

development of the fields of music, sonar,

radar, and speech processing, seismology



Simulation using Matlab



Time & Frequency resolution



Part 3: Multipath in the oceanO -What it Multipath?

- Multipath in the ocean

- Simulation multipath



What is Multipath? O When the transmitter and receiver are at different

locations, the analog of echoes is that the receiver

hears the transmitter's signal, and then hears

echoes caused by the signal traveling different

(usually longer) paths. This is called multipath.



What is Multipath? O Reflection Fadding

O Scaterring Noise

O Diffraction Distortion

Can be a challenging part of any remote-

sensing signal processing system,

including radar, ultrasound, and sonar.



Multipath in the oceanThere may be many bounces of the signal of the seafloor and off the

ocean-air interface (and possibly off other whales or sunken ships,etc.)

Figure : A ship is shown with a sensor array descending from it, an object isdenoted in red (whale? dolphin? submarine?) and the object emits signal x(t),which under goes multipath. The total effect of the multipath is modeled as achannel with impulse response h(t). The ship sonar system receivesz(t)=x(t)*h(t). (Inpractice, the ship really receives z(t)=x(t)*h(t)+n(t), where n(t) issome extra noise.)



Simulation multipathIf we call the line of sight signal x(t)

Then the signal that bounced, received T

seconds later, would be a*x(t-T)

a:(between 1 and -1) accounts for the

attenuation.



Simulation multipath In MATLAB, we will represent this kind of continuous-time impulse response by sampling itwith sampling interval Ts. Then the delay timesT1..Tn are represented as multiples of thesampling interval, so for M samples:

O We need only specify the ak values for k=0...M(assuming we know Ts).

O

Ak will be 0 if there are no delay componentscorresponding to (k)Ts seconds.

O A0 will be 1 for the line of sight signal.



Simulation multipath

Figure 5: This is an example of the impulseresponse for the multipath in a 50 meter water channel (for example, in a bay).



Simulation using Matlab



Time



Spectrogram

spectrogram

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