**Aerosol and HDFLook Exercise #1**

The purpose of these exercises is to become familiar with some of the
MODIS atmosphere products while simultaneously becoming familiar with
some of the HDFLook

functionality.

Throughout this exercise if you see something like this (Plot 
Histogram)

it means use the pulldown menu "Plot" and choose the option "Histogram"

This exercise uses the files

**MOD04_L2.A2001079.0255.005.2006289012028.hdf**

**MOD021KM.A2001079.0255.005.2007232141149.hdf**

Make sure you know how to decode the information contained in the MODIS
file name.

Fill in the following information from the MOD04 file

File date: \_\_\_\_\_\_year \_\_\_\_\_\_ Julian Day \_\_\_\_\_\_\_Month
\_\_\_\_\_\_\_Day

Time of day: \_\_\_\_\_\_\_\_\_\_

Collection: \_\_\_\_\_\_\_\_\_\_

Year of Processing \_\_\_\_\_\_\_\_\_\_

To help get oriented to this granule before exploring the aerosol
product open up the level 1B MODIS HDF file.

*The steps in italics refer to the MOD02 file.*

*The object here is to display the 500 M aggregated to 1Km Reflectance
as an RGB MODIS reprojected image using the Orthographic projection.
Adjust the color contrast to something that is appropriate for this
image*.

*Steps:*

*1. Select the SDS that has the 500 M aggregated to 1 Km Reflectance
data*

*EV_500Aggr1km_RefSB.*

*2. Use the "Set reprojection geometry" button to choose Orthographic*

*3 Select the "Show (RGB) image" underneath the "DUMP DATA ON DISK"
button.*

*We will come back to this file later to explore some of the features of
HDFLook.*

1\. Using HDFLook open up the MODIS file which contains the level 2
aerosol products.

> (Which MOD file? Since it is MOD which sensor is it (Aqua or Terra)?
> There is at least one other way to tell which sensor this is from.
> What is it?)

2.  Choose the SDS which will show AOD for land and Ocean.

> First display this as an SDS image.
>
> If you don't like all of the bright pink then click the "automatic
> mask detection" box back in the main window. Next display this as a
> MODIS reprojected image.

3.  Make sure that both images are displayed in a color palette that
    makes sense to you. Use the pull down menu under "color" in each
    display box and choose a few of the color palettes to try.

4.  For each image use the contrast stretch (HDF_set_stretch window) and
    adjust the contrast so it displays a full range of useful colors.

If you are not sure which "HDF_set_stretch" window corresponds to your
image you can click on "contrast stretch" under the color menu to bring
up the correct one. Take note of the numbers next to the color bar in
the set_stretch window. Now go back to main display window and click on
the "No predefined scaling window." Choose y=ax+b. Notice how the
numbers in the set stretch window change.

Adjust the stretch first by entering values in the low and high cut off
windows.

Next adjust the stretch by using the "Mouse cut-off selection".

Click the button and then drag in the histogram window to choose the
range of values to display.

Note that whenever you change the stretch values the display will not
change until you click the "Apply button"

5\. To make your analysis easier go to the modis-atmos website and find
the image that corresponds to this granule.

Display the RGB image from the MODIS atmos site and AOD images from the
HDFLook window side by side.

6\. Explore the values in the image using (Window  cursor values)

> What is the range of the highest AOD values in the plume at 550?

At 470?

At 2.1?

There are 2 ways to find values in multiple wavelengths. Try both
methods.

> For either method you will have to choose "Cursor values" from the
> "Window" drop down menu in the display window.

*Method A use the pixel value display from the reprojected image*.

*Method B switch to an appropriate SDS. Then enter "\*" in the first
dimension box.*

7\. Plot a transect through a range of values (Plot  Histogram).

> In the drawing window that pops up, use the zoom feature (Drawing_area
>  Zoom) to focus on a useful range of values.

Change the axis values (Settings  Axis settings) to eliminate negative
values and to allow for 2 decimal places on the y axis.

Use the show values feature (Drawing_area  Show values) to find the
exact value of the highest point in your transect.

8\. Why is there a huge gap in the retrieval over the water but not over
the land?

9\. Determine if the plume is dominated by large or small particles.

(which SDS would contain this information?)

10\. Is the plume a smoke or dust plume? How do you know?

11\. How good do you think the aerosol retrieval is in the plume? Why?

12\. What might be some causes for a lack of retrieval over some of the
land areas?

Aerosol and HDFLook Exercise #2

This exercise uses the following file:

MYD04_L2.A2007037.0440.005.2007151015852.hdf

File date: \_\_\_\_\_\_year \_\_\_\_\_\_ Julian day \_\_\_\_\_\_\_Month
\_\_\_\_\_\_\_Day

Time of day: \_\_\_\_\_\_\_\_\_\_

Collection: \_\_\_\_\_\_\_\_\_\_

Year of Processing: \_\_\_\_\_\_\_\_\_\_

Sensor: \_\_\_\_\_\_\_\_\_\_\_\_

1.  Choose the SDS which will show AOD for Ocean only. Display this as
    both an SDS image and a MODIS reprojected image using a rainbow
    color scale.

> Why are the two displays so different?

2.  Use the cursor values to explore both the reprojected and the raw
    image.

> Which image is best for quickly exploring a single parameter (SDS)?
>
> Which image is best for finding values for all of the SDS in the file?

3.  Why is there a big gap in both images?

> 4\. Switch to the grayscale display. Set the contrast stretch to
> improve the image so that it is not too faint nor too bright. Explore
> some of the higher AOD values in the image. What is the highest AOD
> range you can find that you think is not cloud contaminated?

5\. Is the haze over the ocean caused by smoke or dust or a mixture?

6.  Display the SDS for Land AOD.

There are many areas of the land where there is no retrieval. Why?

7.  Use the deep blue retrieval SDS to see if you can get additional
    retrievals over land.

Does deep blue help?

> Since it is easier to have two side by side displays work with your
> neighbor to figure this out.

8\. Deep Blue does not offer a "Small Mode Fraction" SDS. Use the
"Deep_Blue_Angstrom_Exponent_Land" SDS instead. High values (above 1.0)
usually indicate small particles. Is the haze over the land likely to be
smoke, dust or a mixture?