GEOG 216 Midterm Prep Multiple Choice & Short Answer

1200 nm is equivalent to ______ μm.

1.2 μm

0.6 μm is equivalent to ______ nm.

600 nm

How do the terms albedo and spectral reflectance differ from each other?

Albedo refers to total reflectance at all wavelengths, whereas spectral reflectance refers to reflectance at a particular wavelength.

Spectral reflectance refers to the reflectance at ______.

A single wavelength.

Which of the following types of light has the longest wavelength?

Microwave.

Will a lake release photons at a faster rate when it is at 40° F or when it is at 60° F?

When it is at 60° F.

Which normally have higher reflectance?

Younger trees.

Which normally have higher reflectance?

Broadleaf (hardwood) trees.

You are looking at two soils. The first is highly eroded, causing it to be low in organic matter and to have a coarse, sandy texture. The other soil is not eroded, and it is high in organic matter and has a finer texture. Which is likely to be more reflective?

The eroded soil.

You are looking at two soils. The first has a high level of soil moisture, and the other is very dry. Which is likely to appear brighter in a normal color aerial photograph?

The soil that is very dry.

Having high levels of non-organic material (sediment) in water makes it ______ reflective than water with very little nonorganic material.

More.

Which is typically brighter in an aerial photograph: Shallow water or deep water?

Shallow water.

What does the term polarization refer to in radar remote sensing?

The orientation of the antennae used for sending and receiving signals.

You would like to determine the temperature of lava that has been emitted from a volcano. Would radar imagery (e.g., collected using Radarsat-2) be able to give you this information?

No.

Which is likely to have a higher radar return (appear brighter in a radar image)?

The ocean during a storm.

Which side of a hill is typically brighter in a radar image?

The side facing towards the sensor.

A building appears very bright in a radar image. Which of the following is a likely explanation?

The roof is made of metal.

Which of the following applications would light detection and ranging (LiDAR) data be best suited for?

Mapping the heights of buildings.

Which of the following shows the elevation of the bare earth (no trees, houses, etc.)?

Digital terrain model.

Which wavelengths of light do the colors in a false color (a.k.a. color infrared) photograph correspond to?

Red, green, near infrared.

Which wavelength of light does false color film allow you to see that normal color film does not?

Near infrared.

Imagery from the Landsat OLI satellite uses 16-bit DN values, whereas data from the Landsat TM satellite uses 8-bit DN values. Which of the following is an advantage of having 16-bit DN values?

The amount of energy the sensor receives from the ground will be measured more precisely.

In a color image, which three colors can be blended together in different proportions to give you all the colors the human eye can see?

Blue, Green, Red.

You have determined that the scale of an image is 1:20,100. Which of the following are true statements?

1 inch on the image corresponds to 20,100 inches in real life; 1 mm on the image corresponds to 20,100 mm in real life.

1 inch on a 1:8,000 scale image covers a ______ distance on the ground than 1 in on a 1:20,000 scale image.

Greater.

Rayleigh and Mie scattering affect some wavelengths more than others. Which of the following would be scattered the most?

Blue (400/500 nm).

What impact does scattering have on electromagnetic radiation?

It causes its direction to change but not its wavelength.

Scattering makes images collected in visible portion of the spectrum appear ______.

Brighter (it increases the DN values).

You are explaining to a new employee how to identify nuclear power plants in high-resolution imagery, and you tell her that they are always located near bodies of water. What element of image interpretation is this an example of?

Association.

What does the term swath width refer to?

The length of one side of a pixel.

The spatial resolution of the red band on the Sentinel-2 satellite is 10 meters. What does this mean?

Each pixel is 10 meters on a side.

Which of the following satellites has/have a sun-synchronous orbit? Circle all that apply.

AVHRR, VIIRS.

Which is likely to appear brighter in a radar image: A baseball field that is dry or a baseball field that is wet due to a rainstorm?

The wet baseball field.

What is the difference between a sun synchronous orbit and a geosynchronous one?

Sun-synchronous orbiting satellites typically capture images of Earth at the same time every day, while geosynchronous satellites image some areas on Earth 24/7.

What is the advantage of having a geosynchronous orbit?

Geosynchronous orbit allows more timely collection of Earth's images to provide better predictions such as for storms.

Draw a diagram illustrating the difference between a specular and a Lambertian surface.

Specular = leaves at equal opposite angle; Lambertian = uniform reflection in all directions.

What is the difference between a digital terrain model (DTM), a digital surface model (DSM), and a normalized Digital Surface Model (a.k.a., canopy height model)?

DTM is interpolated from the ground return and shows bare earth. DSM is interpolated from the first return and shows heights of natural and manmade objects. NDSM is a derivative elevation product obtained by subtracting DTM from DSM, showing relative height above ground.

When light reaches the atmosphere, it can be absorbed or scattered by the air molecules. What is the difference between absorption and scattering?

Scattering is EMR that interacts with gas molecules and dust particles and is bent. Absorption is EMR in the infrared region causing gas molecules to vibrate.

What is the difference among Rayleigh, Mie, and non-selective scattering?

Rayleigh is radiation that interacts with molecules whose diameter is much shorter than the wavelength. Mie is particles with a diameter about equal to the wavelength. Non-selective is particles with a diameter much larger than the wavelength.

For the following situations please indicate which surface would have a stronger return in a radar image and explain your logic. A. A forest or a grassy pasture. B. Bare soil that has recently been irrigated or bare soil that is very dry. C. The side of Mount Washington towards the sensor or the side of a mountain facing away from it. D. A lake on a windy day or a lake on a calm day. E. A wooden boat or a boat made of metal. F. In a cross-polarized image, a wheat field or a dense, old-growth forest.

A. Forest — reflects more because of its rough surface. B. Dry soil — more moisture makes the soil darker. C. Side facing the sensor — due to topography, the sensor cannot see the side facing away. D. Windy day — the rougher water surface creates more reflection. E. Metal boat — metal is more reflective. F. Old-growth forest — wheat is flatter and reflects less.

Please explain how LiDAR data are collected (you may wish to draw a diagram).

Data is collected by LiDAR sensors using points where height is known. Laser pulses are emitted and the time it takes for the pulses to return is measured to determine elevation.

Please draw a diagram showing how radar data are collected.

Radar sends pulses of energy using radio waves and measures the amount of energy returned. When radar strikes an object about the same size as its wavelength, there is a strong return. If it strikes an object smaller than the wavelength, the radar may pass through.

You have acquired a nighttime image of a volcano that is emitting lava using a digital aerial camera that operates in the visible portion of the spectrum. Please explain why you are able to clearly see the lava but other parts of the scene are not visible.

The visible portion of the spectrum contains light energy that is picked up by digital detectors that generate voltage when energy is received. The lava releases much more visible light energy than the other areas of the scene.

List two ways in which LiDAR differs from radar, and one way in which LiDAR and radar are similar.

LiDAR differs from radar because it emits energy as laser pulses while radar emits energy as radio waves. LiDAR also generally has higher accuracy and resolution than radar because of its shorter wavelength. Both measure the time it takes for the emitted pulse or energy to return.

Which element or elements of image interpretation do you think would be most useful for distinguishing an elementary school from a shopping mall? Please explain your logic. The elements of image interpretation are size, tone, shape, texture, pattern, shadow, site, and association.

Size, shape, and association would be useful. Shopping malls are typically much larger than schools, have different shapes, and schools often have features such as bus loops and playgrounds. Schools are typically found near neighborhoods, while shopping malls are often near other commercial sites.

Which element or elements of image interpretation do you think would be most useful for distinguishing snow from (liquid) lakewater in an aerial photograph similar to the digital aerial photograph you used in Lab 1? Please explain your logic. The elements of image interpretation are size, tone, shape, texture, pattern, shadow, site, and association.

Tone would be useful to distinguish snow from lake water. Using false color, snow will be red and water will be black.

You have obtained an aerial image of a road that has been damaged by a landslide. The length of the damaged part of the road is 0.115" long in the photograph. Based on the known width of the road and the width of the road in the image, you determine that the scale of the photograph near the landslide is 1:12,012. How long is the damaged part of the road in real life? Please give your answer in feet.

115.115 ft.

You have obtained an image of a military base in Russia that contains a tank you have not seen before and you think it may be a new model. Your manager has asked you to determine the dimensions of the tank so it can be further evaluated. To make this measurement you decide to use the distance between railroad rails that are near where the tanks are parked to calculate scale, since you know that in Russia the rails are 1.52 m apart. If the distance between the rails on the photo is 0.136 mm and the length of the tank on the photo is 1.202 mm, please determine: The scale of the aerial image at the railroad track; The length of the tank in real life in meters. A. 1 m = 100 cm, 1 cm = 10 mm.

Scale = 1/11,176.47; Length = 13.43 m.

In the diagram below draw: A. The reflectance curve for a healthy green plant. B. The reflectance curve for soil. C. The reflectance curve for liquid water. D. The reflectance curve for snow.

Healthy green plant: low reflectance in the visible wavelengths, especially in blue and red due to chlorophyll absorption, with high reflectance in near infrared. Soil: generally moderate reflectance that gradually increases with wavelength. Liquid water: very low reflectance, especially in near infrared and shortwave infrared. Snow: high reflectance across visible wavelengths, with decreasing reflectance toward longer wavelengths.

How would the spectral reflectance curve for the green plant you drew for Question 15 change if the plant started to die?

The reflectance curve would drop/change, with lower near-infrared reflectance as the plant becomes less healthy.

How would the soil curve differ if the soil became very wet?

The soil would become less reflective.

On the diagram for Question 16, please label the following: 1. The chlorophyll absorption in the plant spectrum. 2. The feature in the plant spectrum caused by refraction (bending) of the light by the cell walls. 3. The feature in the plant spectrum caused by water in the plant leaf. 4. The feature in the snow spectrum caused by the scattering of EMR by ice crystals.

1. Chlorophyll absorption — mainly in the blue and red portions of the visible spectrum. 2. Cell-wall refraction — the strong increase in reflectance in the near-infrared region (red edge). 3. Water in the leaf — absorption features in the near-infrared/shortwave-infrared region. 4. Ice crystals in snow — high visible reflectance caused by scattering.

QUESTION 18 ON PAPER

Answer is on paper.

QUESTION 19 ON PAPER

Answer is on paper.

Please draw a diagram showing the difference among visible, near infrared, and shortwave infrared light.

Visible light is approximately 400–700 nm; near infrared (NIR) is approximately 700–1,400 nm; shortwave infrared (SWIR) is approximately 1,400–3,000 nm.

What is an atmospheric window? Please explain why atmospheric windows are important.

An atmospheric window is a range of wavelengths that can pass through the atmosphere with relatively little absorption. Atmospheric windows are important because they allow sensors to detect Earth's surface and atmosphere at specific wavelengths, making remote sensing possible.

Please give an example of an application that a LiDAR digital terrain model (DTM) would be better for than a digital surface model (DSM) and explain your reasoning.

A LiDAR DTM would be better than a DSM for monitoring and describing terrain surfaces. This is because DTMs represent only the bare earth, while DSMs include natural and man-made objects on the surface