LABORATORY - VEGETATION REFLECTANCE MODELS

1. Objective:

Lectures have emphasized that a high priority in the advancement of remote sensing science is to develop physical models that link the physical properties of the target medium, through the interaction mechanisms, to the measurement accessible to the satellite or airborne sensor: in the optical region this is the bi-directional reflectance factor (as described in lectures). Vegetation canopies are among the most complicated earth targets to model because we are dealing with canopies made up of individual leaves which have inclinations distributed angularly according to some probability distribution; and in addition, in forests the vegetation is clumped into individual tree crowns which can allow the sensor to view shadows and the soil (or grass background if the density of trees is sufficiently small). We shall refer to the first type model as a turbid medium model and the latter type as an open canopy (clumped vegetation) model. There are numerous such models in the literature, each with their particular assumptions and demands on computing. For this laboratory session, you will run a coupled leaf (PROSPECT) and canopy (SAIL) model to investigate the effects of vegetation parameters on canopy reflectance. In the lectures, we have already talked about these two models. The output of the PROSPECT model is the leaf reflectance and transmittance, which is the required input for the SAIL model. The coupled PROSPECT and SAIL model automatically link these two models together.

Assignment -

1. Investigate the effects of vegetation parameters on canopy reflectance:

(a) The effect of leaf chlorophyll content

Run the model with the following parameters, plot the canopy reflectance with different leaf chlorophyll content and discuss the results.

(b) The effect of leaf water content

Run the model with the following parameters, plot the canopy reflectance with different leaf water content and discuss the results.

(c) The effect of LAI

Run the model with the following parameters, plot the canopy reflectance with different LAI and discuss the results.

(d) The effect of LAD

Run the model with the following parameters, plot the canopy reflectance with different LAD and discuss the results.

2. Analysis of bi-directional reflectance properties of a vegetation canopy

Run the model using the angles along the solar principal plane (the relative azimuth angle is either 0 or 180) to examine the bi-directional reflectance properties. In the model runs, the solar zenith angle is fixed at 30 degrees and the view angles changes from -50 to 50 at the step of 10. The relative azimuth angle is fixed at 180 degrees. With this setting, when the view angle is negative, the sensor faces the sun; while when the view angle is positive, the sun is behind the sensor.

3. Retrieval vegetation properties from remote sensing data

As discussed in the class, a number of vegetation indices have been designed to retrieve leaf area index and leaf chlorophyll content. To do so, these indices have to be highly correlated with LAI or leaf chlorophyll content. Design experiments (similarly to 3.1(a) and 3.1(c)) at nadir view and with solar zenith angle of 30 degrees to test if the following existing indices can be used to retrieve LAI and leaf chlorophyll content. In your report, describe your experiments, results, and discuss the results.

(a) Standard NDVI using wavelengths at 800nm and 680 nm

(b) Modified NDVI using wavelengths at 750 nm and 710 nm

(c) MTVI2

(d) OSAVI/TCARI

Attachment:- Assignment File.rar