Tips about MODIS data

MODIS data comes in many flavours. NASA and partners have created a wealth of datasets based on MODIS data. Here are some tips about what’s out there and what some of the acroymns mean.

Level 1 data are either radiance counts (Level 1A) or calibrated radiances (Level 1B). The former measures the number of photons striking the detectors, the latter is a measure of the energy detected in W/(m2-µm-sr).

Level 2 data are products derived from Level 1 data. These include atmospherically corrected reflectance images (MOD09) and surface temperature (MOD11).

Level 3 data are either produced using modelling to correct or adjust the MODIS input data, or use multiple images for spatial and/or temporal averaging. These include 8-day averages such as the 8-day composite fire product (MOD14A1).

This brings me on to another tip: data from the Terra satellite are called MODXX whilst those from Aqua are MYDXX (XX being a product number).

Few scientists or students will have use for Level 1A data if 1B are available. For many applications data such as the atmospherically corrected MOD09 product may be more appropriate (for example if you want a ‘finished product’ to analyse). MODIS covers a wide swath which introduces distortions towards the edges of the images. Hence the BRDF adjusted nadir product (MCD43A4) may be of interest. Here MCD refers to combined Terra and Aqua data contributing to the product.

At the end of the day though you have to find the data. Google MCD43A4 and a long list of websites, mostly NASA sites, appears. After a couple of days, you may even find a site that allows you access to the data. Or, you could just go to GLOVIS: here you can find Terra, Aqua and Combined products. Simple.

It might be useful to go to the MODIS homepage and browse the product information.

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