The Moderate Resolution Imaging Spectroradiometer (MODIS)
This document provides a basic overview of MODIS satellite data. Additional resources on terminology and fundamentals of remote sensing can be found here and here. and this “review of Selected MODIS Algorithms, Data Products, and Applications”.
Introduction
The Moderate Resolution Imaging Spectroradiometer (MODIS) is an optical sensor onboard two satellites named Terra (originally known as EOS AM-1) and Aqua (originally known as EOS PM-1) operated by NASA. Terra was launched on 18 December 1999 and Aqua was launched on 24 May 2002. Terra’s orbit around the Earth is such that it passes from North to South across the equator in the morning, while Aqua passes South to North over the equator in the afternoon. Terra MODIS and Aqua MODIS take images for the entire Earth’s surface every 1 to 2 days. The data collected is the intensity of the light reflected by earth in 36 different wavelengths (“colors”). Both Terra and Aqua also have other sensors besides MODIS. These two sensors have publicly available daily archive of conditions on the earth surface for the past 20 years!
Spatial and spectral properties
The table below summarized the intended use for cation and corresponding spatial resolution in which they are acquired.
Spectral band number |
Intended use |
Spatial resolution |
|---|---|---|
1-2 |
Land/Cloud boundaries |
250 |
3-7 |
Land/Cloud/Aerosol properties |
500 |
8-16 |
Ocean Color/Phytoplankton/Biogeochemistry |
1000 |
17-19 |
Atmospheric water vapor |
1000 |
20-23 |
Surface/Cloud temperature |
1000 |
24-25 |
Atmospheric temperature |
1000 |
26 |
Cirrus clouds |
1000 |
27-29 |
Water Vapor |
1000 |
30 |
Ozone |
1000 |
31-36 |
Surface/Cloud temperature cloud top altitude |
1000 |
Processing levels
MODIS data is available at different levels of processing.
Level 0: Unprocessed raw satellite feeds (“ungridded orbital swath data”).
Level 1A: Raw un-calibrated swath data with georeference information.
Level 1B: radiometrically calibrated with georeference information.
Level 2: level 1 data atmospherically corrected to yield surface reflectance.
Level 2G: Levcel 2 data calibrated and stored as integers on the sinusoidal tiled gridded system.
Level 3: level 2 data, properly georeferenced, and often temporally composited or averaged. “Best” pixel selection (e.g. one value per pixel over a period of 7 days)
Level 4: data products that have been put through additional processing. Higher processing level than level 3.
More information of these products can be obtain from MODIS Nomenclature.
Products
The higher level data products can be grouped based on their application areas (see: https://modis.gsfc.nasa.gov/data/dataprod/). These products are usually distributed in different spatial resolution (250/500/1000 m) and temporal composite (daily/8-day/16-day/monthly/annual) combinations for both sensors.
Each of those products has a prefix for instance, “MOD” are products from the Terra satellite while “MYD” are products from the Aqua satellite and prefix “MCD” are products generated from a combination of the two satellites.
These products are distributed by different Distributed Active Archive Center(DAAC). For example Land Processes Distributed Active Archive Center, LP DAAC distributes the following products.
MODIS products; # is the product number variant e.g., ‘MOD’, ‘MYD’ or ‘MCD’.
ID |
Name |
ID |
Name |
|---|---|---|---|
1 |
Level-1A Radiance Counts |
20 |
Chlorophyll II Fluorescence |
2 |
Level-1B Calibrated, Geolocated Radiances |
21 |
Chlorophyll a Pigment Concentration |
3 |
Geolocation Data Set |
22 |
Photosynthetically Active Radiation (PAR) |
4 |
Aerosol Product |
23 |
Suspended Solids Concentration in Ocean Water |
5 |
Total Precipitable Water |
24 |
Organic Matter Concentration |
6 |
Cloud Product |
25 |
Coccolith Concentration |
7 |
Atmospheric Profiles |
26 |
Ocean Water Attenuation Coefficient |
8 |
Gridded Atmosphere Products (Level-3) |
27 |
Ocean Primary Productivity |
9 |
Atmospherically Corrected Surface Reflectance |
28 |
Sea Surface Temperature |
10 |
Snow Cover |
29 |
Sea Ice Cover |
11 |
Land Surface Temperature & Emissivity |
31 |
Phycoerythrin Concentration |
12 |
Land Cover/Land Cover Change |
35 |
Cloud Mask |
13 |
Vegetation Indices |
36 |
Total Absorption Coefficient |
14 |
Thermal Anomalies, Fires and Biomass Burning |
37 |
Ocean Aerosol Properties |
15 |
Leaf Area Index and FPAR |
39 |
Clear Water Epsilon |
16 |
Surface Resistance & Evapotranspiration |
43 |
Albedo 16-Day Level-3 |
17 |
Vegetation Production, Net Primary Productivity |
44 |
Vegetation Cover Conversion & Continuous Fields |
18 |
Normalized Water Leaving Radiance |
ALB |
Snow and Sea Ice Albedo |
19 |
Pigment Concentration |
File format
MODIS data is stored in “Hierarchical Data Format - Earth Observation System” (HDF-EOS) files. HDF format was developed to support storing multiobject data sets (subdatasets) within one file (container). These subdatasets can include raster images, tables, scientific data sets (multidimensional arrays), annotations, vector files, palette information and many more formats.
Read more about use of HDF in NASA Earth Observation System data in HDF-EOS Information Center.
Converting HDF files to a common format (e.g. GeoTiff) that can be read across different software libraries has been one of the major challenges with MODIS data processing. Until recently, commercial programs like ArcGIS, ENVI were not able to read and explore HDF files. In the next section we will show how you can use R to search, download and process MODIS data..
Geographic information
Each file stores data for an area of 10 by 10 degrees, using the sinusoidal coordinate reference system.
Tiling Scheme
The tiles are identified using rows “h” (for horizontal) and columns “v” (for vertical). MODIS uses a vertical horizontal tiling systems (e.g.tile h09v04 as shown in the figure below. A kmz file with MODIS Tile boundaries can be found here
MODIS tiles indexed horizontally and vertically
MOD09A1 product
Now let’s look at an example MODIS surface reflectance product. “MOD09A1” is a surface reflectance product from data acquired by the MODIS sensor onboard the Terra satellite — hence the prefix “MOD”. It provides estimated “target at surface” spectral reflectance values that have been calibrated for atmospheric conditions such as gasses, aerosols, and Rayleigh scattering. Global surface reflectance products can be obtained at either 250 m or 500 m spatial resolution, and as as daily or 8-day composite data. Below we show a table of the characteristics of the 13 layers that come with “MOD09A1”. A more in-depth description is available here.
MODIS products
Band |
Name |
Type/units |
Data Type |
Fill value |
Valid Range |
Scale fact |
|---|---|---|---|---|---|---|
1 |
Red (620-670 nm) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
2 |
NIR (841-876 nm) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
3 |
Blue (459-479 nm) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
4 |
Green (545-565 nm) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
5 |
NIR (1230-1250 nm) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
6 |
SWIR (1628-1652) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
7 |
SWIR (2105-2155 nm) |
Reflectance |
16-bit signed integer |
28672 |
-100 - 16000 |
0.0001 |
8 |
Reflectance Band Quality |
Bit Field |
32-bit unsigned integer |
4294967295 |
NA |
NA |
9 |
Solar Zenith Angle |
Degree |
16-bit signed integer |
0 |
0 - 18000 |
0.01 |
10 |
View Zenith Angle |
Degree |
16-bit signed integer |
0 |
0 - 18000 |
0.01 |
11 |
Relative Azimuth Angle |
Degree |
16-bit signed integer |
0 |
-18000 - 18000 |
0.01 |
12 |
500 m State Flags |
Bit field |
16-bit unsigned integer |
65535 |
NA |
NA |
13 |
Day of Year |
Julian day |
16-bit unsigned integer |
65535 |
1 - 366 |
NA |