- 1a. What is a biome?
1b. What factors define the extent of a particular biome?
1c. Do species diversity and richness tend to increase moving from the poles to the equator? How about from high altitudes to lower altitudes?
2a. What factors affect reflectance, transmittance and scattering of radiation in a canopy?
2b. List some canopy properties that can be measured, either directly or indirectly, using remote sensing techniques.
2c. List some advantages of using radar remote sensing techniques as opposed to passive optical techniques.
3a. What are two primary ways in which plants respond to stress?
3b. What is vapor pressure deficit and how does it affect photosynthetic rates?
3c. What is leaf water potential and what information about plant stress can be inferred from its measurement?
4a. Describe vegetation dynamics over daily, seasonal, and long-term time periods.
5a. What is a spectral vegetation index and what is it used for?
5b. Which two portions of the electromagnetic spectrum are typically used to calculate spectral vegetation indices? Why?
5c. What is an advantage of the normalized difference vegetation index (NDVI) compared to the simple ratio index?
6a. What range of wavelengths is photosynthetically active radiation (PAR) restricted to?
6b. How is light use efficiency calculated and what does it indicate?
ANSWERS
1a. A biome can be defined as a broad grouping of distinctive plant formations. See Section 1.
1b. Regional or global extents of various biomes depend on climate and weather conditions including temperature and precipitation patterns, and physiographic barriers such as mountains and oceans. See Section 1.
1c. Generally, species diversity and richness increase going from the poles to the equator, and from high elevations to low elevations. See Section 1.1.
2a. Reflectance, transmittance and scattering of radiation in a canopy are affected by (1) vegetation structure and (2) optical properties (spectral reflectance and transmittance) of leaves or needles. See Section 1.2.
2b. Canopy reflectance, leaf area index, crown cover or closure, biomass, height, and architecture. See Section 2.
2c. Radar has the advantage of being able to be used day or night, and during cloudy or hazy atmospheric conditions. See Section 2.3.1.
3a. Plants may respond to stress primarily by the amount of developed foliage and control of the stomatal openings (pores) on leaves. See Section 3.
3b. Vapor pressure deficit (VPD) is the difference in vapor pressure inside and outside a leaf, and essentially is an index of the drying capacity of the air, which varies with temperature and humidity conditions. When the VPD becomes too large, the plant's stomata close and photosynthesis is slowed or stopped. See Section 3.2.
3c. Leaf water potential is a measure of how tightly or strongly a leaf holds its moisture. A high leaf water potential value indicates that a plant may be experiencing water stress.
4a. On a daily basis, leaf orientation changes in response to the sun's movement and water stress. Over seasonal time durations, variations such as growth, greening up, flowering, senescence and shedding of leaves occur. Long-term dynamics include changes in the spatial distributions of plant species, usually due to changes in environmental conditions (natural and human induced). See Section 4.
5a. A spectral vegetation index (SVI) is generated by combining data from multiple spectral bands into a single value. SVIs are designed to enhance the vegetation signal while minimizing the response of various background materials, providing an approximate measure of live, green vegetation amount. See Section 5.
5b. Spectral vegetation indices are usually calculated using an infrared wavelength and a red (or combined visible) wavelength. Green leaves have a distinct spectral reflectance pattern in the red or visible and near-infrared wavelengths which can be exploited to distinguish the spectra of green vegetation from those of soil and other natural and manmade materials. See Section 5.
5c. The calculation of the normalized difference vegetation index (NDVI) reduces the effects of variable irradiance (illumination) levels. See Section 5.2.
6a. Photosynthetically active radiation (PAR) is restricted to the portion of sunlight's spectrum ranging from 0.4 to 0.7 micrometers (µm) which is comparable to the range of light the human eye can see. See Section 6.1.
6b. Light use efficiency (LUE) is the ratio of net primary production (NPP) to absorbed photosynthetically active radiation (APAR). LUE indicates how efficiently a plant produces biomass (NPP) for a given amount of absorbed PAR. See Section 6.2.
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