Digital Filters
What is a high pass filter?
A filter that passes high frequencies and blocks the lows.
frequency modulation
How are colored images represented digitally? (What does the computer see it as?
Each pixel consists of three numbers from 0 to 255 representative of the red, green, and blue value of that pixel.
Name one application of radar.
[multiple answer acceptable]
autonomous vehicles, air traffic control, weather tracking, military surveillance, radar guns,...
Give a fun fact you learned from another team's project.
[multiple answers acceptable]
What is a notch filter and when might you use one?
A notch filter filters out a single frequency or very small bandwidth. You might use one to filter out clutter in radar or filter out the 60 Hz tone that electronics see when plugged into a wall.
Which is typically larger, a communication signal's carrier frequency or its modulation frequency?
How does edge detection work in image processing?
Kernels are used that check for contrast between a light-dark-light or dark-light-dark sequence of pixels.
How does a radar "look" in a certain direction?
It uses a phased array antenna. By combining the observed signals from each element with certain delays, we can beamform to look in a certain direction.
Name some of the classes of objects that Michael tried to use a radar to distinguish between.
pedestrians, cars, birds, drones, other
In Python, we used signal.butter(), signal.ellip(), signal.cheby1(), and signal.bessel(). Why are the differences between these filters?
The provide filters with different characteristics. For example, the Bessel and Butterworth provide filters with flat passbands but less steep cutoffs. The Elliptic and Chebyshev provide filters with sharp cutoffs but ripples in the passband.
Describe frequency shift keying (FSK).
FSK consists of sending different frequencies to describe the different symbols in a coding system.
How do you blur an image?
Use a moving average kernel. In 2D convolution terms, make your kernel all 1/#kernel cells.
Describe the Doppler effect and how radar uses it.
The Doppler effect is how an observed frequency is increased if the source is moving toward the observer and decreased if away. Radar uses Doppler shift to determine the velocity of things it senses in its environment.
What color were the bones in the images Lauren showed us on Wednesday?
They were dark. She informed us this is a key characteristic of MRI images.
Which filter type has ripples in the passband (range of frequencies that pass through the filter) and the stopband (range of frequencies that gets blocked)?
Elliptic
Which is at a lower carrier frequency, AM radio or FM radio?
Why is that radio type at a lower frequency?
Amplitude modulation, or AM, is at a lower carrier frequency (100s of kHz vs FM's ~100 MHz).
AM modulation is usually used for news since it is more susceptible to noise and people will tolerate noise in the news more than music. News radio stations also typically desire their signals to travel further (low frequency = farther travel distance).
What is a segmentation filter?
It restricts your filtered image to have only a smaller discrete number of colors such as 0 (black) and 255 (white). It works by setting a threshold and calculating new pixel values by comparing the input pixel values to these thresholds.
When we looked at real radar data, which component of Ryder appeared to have the largest Doppler/velocity during his stationary walking? Which component had a stronger return or power in comparison?
His arms had larger Doppler/velocity. His legs had less velocity but stronger return.
Why do we need to think about ethics as engineers, researchers, and technologists?
Once you open the can of new technology, it's hard to put it away and regulate. Facial recognition software is a prime example, and it has proven to have many important misuses.
If we design out own filter, we can place zeros and poles on the unit circle to define its frequency response. What does placing a zero on the unit circle do?
It pulls the corresponding frequency down. In other words, it notches out that frequency in the resultant filter.
What is the difference between modulation and encoding.
Modulation is the act of changing a carrier frequency to contain information.
Encoding is using modulation techniques to define different code words or symbols.
Mathematically, how does 2D convolution (image filtering work) in your own words?
You take a kernel and use it to apply a weight to surrounding pixels. Then once surrounding pixels are weighed, you sum everything together and that results in your new pixel value. You then have to move to the net pixel and repeat this process to get the full new image.
The range of an object is determined by the radar by calculating what?
Range = (speed * time)/2
The signal must travel to the object and back in the observation time, thus giving us the 2.
What technology is responsible for allowing us to image the surface of planets?
Synthetic aperture radar (SAR)