electromagnetic modeling for lidar and landsat remote sensing...

MotivationModels

Examples

Electromagnetic Modeling for Lidar and Landsatremote sensing of forests

Leland Pierce

The Univ of Michigan, Radiation LabAnn Arbor, MI 48109-2122 USA

May 7, 2014

Pierce Electromagnetic Modeling

MotivationModels

Examples

Scenario

Continuing from the previous presentation...

I Let’s say we are a researcherinterested in biodiversity andhabitat.

I We know forest structurematters, among other things.

I The sensors are somewhatsensitive to forest structuralattributes

I How do we use the sensors toget at biodiversity?

(Photos Courtesy of Kathleen Bergen)


MotivationModels

Examples

Parameter Estimation Procedure

I Since there are no “standard products” for forest structure,each researcher must estimate these.

I Regressions seem the most straighforward way.

I An alternative is to use physics-based models.

I These can provide intuition as to what is possible.

I ...and enable the intelligent use of the remotely-sensed data.


MotivationModels

Examples


I Today I will provide an overview of the basic physics behindthese models.

I I will also discuss the approximations that are used, and theirpossible effects on the results.

I You will see that these are straightforward to use.

I Simulations of forests relevant to your research area canprovide clues as to how to use the measured remotely-senseddata effectively to get the structural parameters you need.


MotivationModels

Examples

Outline

1. Forest Geometrical Model

2. Interaction of Light with Matter

3. Ray Tracing

4. Radiative Transfer: Landsat

5. Lidar


MotivationModels

Examples

Fractal Tree Model

I Model developed in late 1990’s.

I Fractal pseudo-random trees.

I Use Lindenmayer System:string-rewriting rules are used togenerate realistic branchingstructures, with needles andleaves.

I Each species of tree has its ownset of rules so it looks realistic.

I Both coniferous and deciduoustrees can be modeled.


MotivationModels

Examples

Fractal Tree Model

Same tree with and without leaves:


MotivationModels

Examples

Interaction of Light with Matter

3 mechanisms:

1. reflection

2. absorption

3. transmission

Conservation of Energy:Incident Energy = Energy Reflected + Energy Absorbed + Energy Transmitted


MotivationModels

Examples

Raytracing

Can calculate how much of the incident energy is redirected ineach direction:

I PROSPECT is oneexample for leaves.

I Can do the same forstems, twigs, needles,bark, etc.

I Approximate withthousands of rays

Jacquemoud, Baret, “PROSPECT: A Model of Leaf Optical Properties Spectra”, Rem Sens Env, 1990.


MotivationModels

Examples

Radiative Transfer

For Landsat-type sensors implement the following algorithm:

I Keep track of the energy as itpropagates along each of the rays.

I Track rays through several bouncesuntil their energy is very small.

I Repeat for every object in the canopy.

I Also include the reflection from theground.

I Add up all the energy directed at oursensor.

And repeat this for every wavelength of interest. (Tree image courtesy of clipart.com)


MotivationModels

Examples

PROSAIL

I PROSAIL uses statistical properties of forestsI The fractal forest can be used to calculate these statistics:

I branch angle distribution,I leaf size distribution,I leaf angle distribution,I branch sizes,I densities, LAI, etc.


MotivationModels

Examples

Landsat-type Example

This example shows the change in the spectrum as the forest LAIis varied, as calculated by PROSAIL.

Plot from: Jacquemoud, Verhoef, Baret, Bacour, Zarco-Tejada, Asner, Francois,Ustin, “PROSPECT+SAIL models: A review of use for vegetation characterization,”Rem Sens Env, 2009.


MotivationModels

Examples

Lidar Model

Forest Attributes:

Biomass

Tree Species

Tree Attributes:

Height

Crown Diameter

Height to live crown

Trunk Diameter


MotivationModels

Examples

LIDAR Model

I Divide volume of stand into cubes.

I Each cube analyzed for verticalreflection and transmission.

I track the first reflection only (a firstapproximation)

I Radiative Transfer from cube-to-cubeto produce time-trace of LIDAR signal.

I Horizontal Gaussian pulse weightingacross the stand, with a verticalGaussian as well to obtain verticalresolution.


MotivationModels

Examples

Radiative Transfer for one cube

I Given power propagating from aboveand below: quantify how muchtransmitted and reflected in eachdirection.

I Update the power propagating to nextcubes.

I Can use PROSPECT or measurementsfrom literature to determine values forreflection and transmission forleaves/needles and branches.


MotivationModels

Examples

Radiative Transfer for one column

I Light is tracked as it propagatesdown and then up a single column ofcubes.

I At each time step one cube istraversed, with both a downgoingand an upgoing light power value.

I Ground reflectance is approximatedbased on data in literature.

I The upgoing light at the top of thecanopy is the reflected LIDAR signal.


MotivationModels

Examples

Short Trees


MotivationModels

Examples

Medium Trees


MotivationModels

Examples

Tall Trees


MotivationModels

Examples

Low Biomass


MotivationModels

Examples

Medium Biomass


MotivationModels

Examples

High Biomass


MotivationModels

Examples


One possible way of using modeling for parameter estimation:


MotivationModels

Examples

Thanks for your attention

You can contact me at:[email protected]

Viewgraphs available at:http://www.eecs.umich.edu/~lep/lidar optical talk 2014.pdf

or:

http://tinyurl.com/lep2014models


electromagnetic modeling for lidar and landsat remote sensing...

Documents