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2. AERSURFACE

2.1. Introduction

In this section, we will cover AERSURFACE, a preprocessor for AERMET that assists in characterizing land surface parameters. It defines three key values:

Surface roughness length (Zo)
Albedo (Alb)
Bowen ratio (Bo)

Task	Assist in obtaining values that characterize land use and land cover.
Input Data	Land cover, impervious surface percentage, and canopy percentage in GeoTIFF format.
Output Data	Surface roughness length (Zo), albedo, and Bowen ratio — to be used in AERMET.

Parameter	Definition	Usage
Surface Roughness (Zo)	A measure of terrain roughness — how much resistance the surface offers to wind flow due to obstacles like vegetation, buildings, and topography.	Defines the wind speed profile near the surface. Higher Zo generates more turbulence, which affects pollutant dispersion.
Albedo (Alb)	The proportion of solar radiation reflected by the surface. Ranges from 0 (fully absorbed) to 1 (fully reflected).	Affects soil heating and, consequently, convective turbulence (rising warm air bubbles).
Bowen Ratio (Bo)	The ratio between sensible heat (air heating) and latent heat (evaporation). It indicates whether heat is transferred more into the air or into evaporation.	Helps estimate surface heat flux, which is essential for calculating atmospheric stability (how well the air supports pollutant dispersion).

2.2. Download the Executable

First, download the AERSURFACE executable:

AERSURFACE - EPA SCRAM

Download the appropriate file for your operating system and save it to: ..\AermodTutorial\AERSURFACE\

In Figure 1 we can observe the download page.

Figure 1

Figure 1: Download the AERSURFACE executable according to its specifications in English.

2.3 Obtaining Surface Data

Go to: MRLC Viewer. Close the pop-up window as shown in Figure 2.

Figure 2

Figure 2: MRLC Viewer

Enable only the National Atlas States and ESRI World Imagery layers. See Figure 3.

Figure 3

Figure 3: Enabling relevant layers for download.

Use your mouse to pan and zoom to the USA, then locate the correct state. See Figure 4.

Figure 4

Figure 4: Zoom into the region of interest.

Next, locate the point -88.9520 40.4471 using the mouse coordinates. See Figure 5.

Figure 5

Figure 5: Pinpointing the central point of the area.

Zoom in further as shown in Figure 6.

Figure 6

Figure 6: Further zoom for selection accuracy.

Click the icon shown, and using the left mouse button, select your area of interest by clicking the two corner points. See Figure 7 and Figure 8.

Figure 7

Figure 7: Activate the selection tool.

Figure 8

Figure 8: Example of a selected urban and rural area.

Check the boxes exactly as shown, and set Select Years to 2023. See Figure 9.

Figure 9

Figure 9: Configure the download options.

Enter your email and click download. See Figure 10.

Figure 10

Figure 10: Enter your email to receive the download link.

Check your inbox for a message from no-reply@usgs.gov and click the download link. See Figure 11.

Figure 11

Figure 11: Email with the download link.

Save the downloaded ZIP file to: C:\Users\Cliente\Desktop\AermodTutorial\1.AERSURFACE Then extract its contents.

2.4 Preparing AERSURFACE Inputs

Rename the .tiff file to landcover.tiff. See Figure 12.

Figure 12

Figure 12: Rename the TIFF to landcover.tiff.

Create a new text file named AERSURFACE.txt. COMO MOSTRADO NO CODIGO ABAIXO:

CO STARTING

   TITLEONE  UFSC/ TraPoDisO
   TITLETWO  Bloomington, IL, 2024 NLCD w/ Impervious and Canopy

   OPTIONS   PRIMARY ZORAD
   DEBUGOPT  GRID TIFF

   CENTERLL   40.48  -88.99   NAD83

   DATAFILE  NLCD2011  "landcover.tiff"

   CLIMATE   AVERAGE   SNOW   NONARID

   FREQ_SECT MONTHLY  2  NONAP

   SECTOR   1   135   225
   SECTOR   2   225   135 

   SEASON   WINTERNS   11  12  1
   SEASON   WINTERWS   2   3
   SEASON   SPRING     4   5   6
   SEASON   SUMMER     7   8   9
   SEASON   AUTUMN    10
   RUNORNOT  RUN 

CO FINISHED

OU STARTING

   SFCCHAR    "BL_2024_Imp_Can.sfc"
OU FINISHED

Below is an explanation of each command in the file:

`CO STARTING` – Begins the control block.
`TITLEONE`, `TITLETWO` – Custom titles for identification in output files.
`OPTIONS PRIMARY ZORAD` – Requests default outputs and directionally-resolved Zo.
`DEBUGOPT GRID TIFF` – Enables extra debug output (grid and TIFF info).
`CENTERLL 40.48 -88.99 NAD83` – Geographic center of analysis.
`DATAFILE NLCD2011 landcover.tiff` – Defines land cover classification and file.
`CLIMATE AVERAGE SNOW NONARID` – Local climate parameters.
`FREQ_SECT MONTHLY 2 NONAP` – Monthly values, 2 directional wind sectors.
`SECTOR 1 135.00 225.00` – Sector 1 definition (SE–SW).
`SECTOR 2 225.00 135.00` – Sector 2 definition (SW–N–SE).
`SEASON WINTERNS 1 11 12` – Late Autumn/Winter season.
`SEASON WINTER 2 3` – Winter with snow.
`SEASON SPRING 4 5 6` – Transitional Spring.
`SEASON SUMMER 7 8 9` – Midsummer.
`SEASON AUTUMN 10` – Autumn with unharvested crops.
`RUNORNOT RUN` – Executes the processing.
`CO FINISHED` – Ends the control block.
`OU STARTING` – Output file section.
`SFCCHAR BL_2024_Imp_Can.sfc` – Output file name.
`OU FINISHED` – Ends the output section.

2.5 Running AERSURFACE

Open the Command Prompt and navigate to the folder: cd C:\Users\Cliente\Desktop\AermodTutorial\1.AERSURFACE See Figure 14.

Figure 14

Figure 14: Open the terminal in the correct directory.

Then type the following to execute AERSURFACE: aersurface aersurface.txt

If successful, it should display output like in Figure 15.

Figure 15

Figure 15: Console output when execution completes.

2.6. AERSURFACE Output

Once complete, the .sfc file will be created — this contains the surface data. See Figure 16.

Figure 16

Figure 16: Surface file created after successful execution.

The following lines are an example of a surface characteristics file used by AERMET. Each line provides monthly values of albedo, Bowen ratio, and surface roughness length for a specific wind direction sector.

Example:

**           Month    Sect    Alb      Bo        Zo
   SITE_CHAR    1       1     0.18     0.95     0.317
   SITE_CHAR    1       2     0.18     0.95     0.346
   SITE_CHAR    2       1     0.46     0.49     0.250
   SITE_CHAR    2       2     0.46     0.49     0.273
   SITE_CHAR    3       1     0.46     0.49     0.250

Column Descriptions

Column	Description
SITE_CHAR	Keyword indicating the start of a surface characteristics entry.
Month	Month of the year (1 = January, 2 = February, etc.).
Sect	Wind direction sector number. Defined in AERMET configuration.
Alb	Albedo — fraction of solar radiation reflected by the surface.
Bo	Bowen Ratio — ratio of sensible heat flux to latent heat flux. Reflects surface moisture conditions.
Zo	Roughness Length (in meters) — describes the aerodynamic roughness of the surface, affecting wind profile near the ground.

Example Interpretation

For the line:

SITE_CHAR    1       1     0.18     0.95     0.317

This means:

Month: January
Sector: 1 (e.g., wind directions between 135° and 225°, if there are two sectors)
Albedo: 0.18
Bowen Ratio: 0.95
Roughness Length (Zo): 0.317 meters

These values are used by AERMET to compute atmospheric stability and turbulence based on the physical characteristics of the surface surrounding the meteorological station.

Save this file to the folder C:\Users\Cliente\Desktop\AermodTutorial\3.AERMET: It will be used in AERMET's Stage 2 as a surface input.

2.7 Next Step

After finishing this step, you can continue to: AERMINUTE

2.7 ANEXOS

Para efeito de comparação ou caso possua alguma divergência do que foi descrito aqui, disponibilizamos o arquivo aermetComplete.rar

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