Moderate Resolution Imaging Spectroradiometer (MODIS)

NASA's Land, Atmosphere Near real-time Capability for EOS (LANCE)-Moderate Resolution Imaging Spectroradiometer (MODIS) has released an improved version, Collection 6.1 (C6.1), for all MODIS Level-1 (L1) and higher-level Level-2 (L2) & Level-3 (L3) Atmosphere Team products.

The decision to create a new improved Collection 6.1 was driven by the need to address a number of issues in the current Collection 6 Level-1B (L1B) data. These L1B issues had a negative impact in varying degrees in downstream MODIS Atmosphere Level-2 (L2) and Level-3 (L3) products.

All MODIS L1 and Atmosphere product users are encouraged to switch over to the C6.1 products. Please note the change in URL from allData/6 to allData/61. Users who use a script to download data will need to adjust their script.

• NRT3 URL for C6.1 products is https://nrt3.modaps.eosdis.nasa.gov/archive/allData/61/
• NRT4 URL for C6.1 products is: https://nrt4.modaps.eosdis.nasa.gov/archive/allData/61/

The C6 L1 and atmosphere products will continue in parallel with the C6.1 collection processing and be made available on https://nrt3.modaps.eosdis.nasa.gov/archive/allData/6/ until the end of November 2017, at which time, only C6.1 of Terra- and Aqua-MODIS L1 and atmosphere NRT products will be available.

Collection 6.1 Land Products

Starting in November 2017, C6 Land processing stream will use the C6.1 L1B as input, with no change to the land science processing algorithms. We do not expect to see any significant impact to most of the land products by using upstream C6.1 as inputs except for some minor differences in Terra MODIS snow and sea-ice products because of differences in the Terra cloud mask. Therefore C6 processing of NRT Terra- and Aqua-MODIS Land products will continue until sometime next year (probably around middle of 2018) when C6.1 processing of Land products will start. Therefore, NRT MODIS Land product users should continue to use C6 product at https://nrt3.modaps.eosdis.nasa.gov/archive/allData/6 or https://nrt4.modaps.eosdis.nasa.gov/archive/allData/6.

For a complete list of available C6 and C6.1 Terra- and Aqua-MODIS products, please visit: https://lance3.modaps.eosdis.nasa.gov/data_products/ or https://lance4.modaps.eosdis.nasa.gov/data_products/.

To review updates to C6.1 L1 and Atmosphere products, please visit the MODIS Atmosphere Team page.

The MODIS Corrected Reflectance imagery is only produced in near real-time. It was developed to provide natural-looking images by removing gross atmospheric effects such as Rayleigh scattering from the visible bands. By contrast, the Surface Reflectance (SR) product is available in near real-time and as a standard product. Surface Reflectance provides a more complete atmospheric correction algorithm that includes aerosol correction and is designed to derive land surface properties. In clear atmospheric conditions the corrected reflectance product is similar to the SR product but they depart from each other in the presence of aerosols.

Band Combinations

MODIS (Terra/Aqua) Corrected Reflectance (True Color)

True Color: Red = Band 1 (670nm), Green = Band 4 (565nm), Blue = Band 3 (479nm)

These images are called true-color or natural color because this combination of wavelengths is similar to what the human eye would see. The images are natural-looking images of land surface, oceanic and atmospheric features. The downside of this set of bands is that they tend to produce a hazy image. This layer is similar to the VIIRS Corrected Reflectance Bands I1, M4, M3 layer.

MODIS (Terra/Aqua) Corrected Reflectance (Bands 7, 2, 1)

False Color: Red = Band 7 (2155 nm), Green = Band 2 (876 nm), Blue = Band 1 (670 nm)

This combination is most useful for distinguishing burn scars from naturally low vegetation or bare soil and enhancing floods. This combination can also be used to distinguish snow and ice from clouds. Snow and ice are very reflective in the visible part of the spectrum (Band 1), and absorbent in Bands 2 (near infrared) and 7 (short-wave infrared, or SWIR). Thick ice and snow appear vivid sky blue, while small ice crystals in high-level clouds will also appear blueish, and water clouds will appear white. This layer is similar to the VIIRS Corrected Reflectance Bands M11, I2, I1 layer.

The MODIS Corrected Reflectance imagery is available only as near real-time imagery. The imagery can be visualized in Worldview and the Global Imagery Browse Services (GIBS). The sensor resolution is 500 m and 250 m (Bands 1 and 2 have a sensor resolution of 250 m, Bands 3 – 7 have a sensor resolution of 500 m, and Bands 8 - 36 are 1 km. Band 1 is used to sharpen Band 3, 4, 6, and 7), imagery resolution is 250 m, and the temporal resolution is daily.

Applications of MODIS Corrected Reflectance (Bands 7, 2, 1)

Colors

Vegetation: Green

Water: Black or dark blue

Desert/Naturally bare soil: Sandy pink

Burn scar: Red to reddish-brown, depending on the nature of the pre-fire vegetation and the severity of the burn.

Vegetation and bare ground

Vegetation is very reflective in the near infrared (Band 2), and absorbent in Band 1 and Band 7. Assigning that band to green means even the smallest hint of vegetation will appear bright green in the image. Naturally bare soil, like a desert, is reflective in all bands used in this image, but more so in the SWIR (Band 7, red) and so soils will often have a pinkish tinge.

Burned areas

Burned areas or fire-affected areas are characterized by deposits of charcoal and ash, removal of vegetation and/or the alteration of vegetation structure. When bare soil becomes exposed, the brightness in Band 1 may increase, but that may be offset by the presence of black carbon residue; the near infrared (Band 2) will become darker, and Band 7 becomes more reflective. When assigned to red in the image, Band 7 will show burn scars as deep or bright red, depending on the type of vegetation burned, the amount of residue, or the completeness of the burn.

Water

Liquid water on the ground appears very dark since it absorbs in the red and the SWIR. Sediments in water appear dark blue. Ice and snow appear as bright turquoise. Clouds comprised of small water droplets scatter light equally in both the visible and the SWIR and will appear white. These clouds are usually lower to the ground and warmer. High and cold clouds are comprised of ice crystals and will appear turquoise.

MODIS (Terra) Corrected Reflectance (Bands 3, 6, 7)

False Color: Red = Band 3 (479 nm), Green = Band 6 (1652 nm), Blue = Band 7 (2155 nm)

This combination is used to map snow and ice. Snow and ice are very reflective in the visible part of the spectrum (Band 3), and very absorbent in Bands 6 and 7 (short-wave infrared, or SWIR). This band combination is good for distinguishing liquid water from frozen water, for example, clouds over snow, ice cloud versus water cloud; or floods from dense vegetation. This band combination is only available for MODIS (Terra) because 70% of the band 6 sensors on the MODIS instrument on the Aqua satellite failed shortly after launch. This layer is similar to the VIIRS Corrected Reflectance Bands M3, I3, M11 layer.

Applications of MODIS Corrected Reflectance (Bands 3, 6, 7)

Colors

Vegetation: Green

Ice or snow: Red

Liquid water on the ground: Black or dark red

Liquid water clouds: White

Ice clouds: Peach

Desert: Light blue-green

Snow and Ice

Since the only visible light used in these images (Band 3) is assigned to red, snow and ice appear bright red. The more ice, the stronger the absorption in the SWIR bands, and the more red the color. Thick ice and snow appear vivid red (or red-orange), while small ice crystals in high-level clouds will appear reddish-orange or peach.

Vegetation

Vegetation will appear green in this band combination, as vegetation is absorbent in Bands 3 and 7, but reflective in Band 6. Bare soil and deserts will appear bright cyan in the image since it much more reflective in Band 6 and 7 than Band 3.

Water

Liquid water on the ground will appear very dark since it absorbs in the red and the SWIR, but small liquid water drops in clouds scatter light equally in both the visible and the SWIR, and will therefore appear white. Sediments in water appear dark red.

The MODIS Surface Reflectance products provide an estimate of the surface spectral reflectance as it would be measured at ground level in the absence of atmospheric scattering or absorption. Compared to Corrected Reflectance imagery, the MODIS Land Surface Reflectance product (MOD09) is a more complete atmospheric correction algorithm that includes aerosol correction, and is designed to derive land surface properties. In clear atmospheric conditions the Corrected Reflectance product is very similar to the MOD09 product, but they depart from each other in presence of aerosols.

Layers visible in GIBS and Worldview include:

MODIS (Terra/Aqua) Land Surface Reflectance (True Color)

True Color: Red = Band 1 (670 nm), Green = Band 4 (565 nm), Blue = Band 3 (479 nm)

These images are called true-color or natural color because this combination of wavelengths is similar to what the human eye would see. The images are natural-looking images of land surface, oceanic and atmospheric features.

MODIS (Terra/Aqua) Land Surface Reflectance (Bands 7, 2, 1)

False Color: Red = Band 7 (2155 nm), Green = Band 2 (876 nm), Blue = Band 1 (670 nm)

This combination is most useful for distinguishing burn scars from naturally low vegetation or bare soil and enhancing floods. Vegetation will appear green and burned areas will appear reddish.

MODIS (Terra/Aqua) Land Surface Reflectance (Bands 1, 2, 1)

False Color: Red= Band 1 (670 nm), Green = Band 2 (876 nm), Blue = Band 1 (670 nm)

Vegetation is very reflective in the near infrared (Band 2), and absorbent in Band 1. Assigning band 2 to green means even the smallest hint of vegetation will appear bright green in the image. Liquid water on the ground will be very dark since it absorbs in the red and the SWIR and sediments in water appear pink. This band combination is good for identifying vegetation changes, drought and floods. This layer is only available as a Surface Reflectance layer, there is no corrected reflectance version of this layer.