Moderate Resolution Imaging Spectroradiometer (MODIS)

About Collection 6.1

MODIS Collection 6.1 (C61) addresses known issues and inconsistencies in the C6 L1B products, revealed by the MODIS Calibration Science Team (MCST), after the completion of the C6 reprocessing and hence most C61 land NRT products are largely identical to C6 equivalents, barring small changes introduced by the changes in L1B. The only other notable change in C61 has been a correction to flagging of some high-aerosol areas, in the L2 Land Surface-Reflectance (LSR) that is mostly seen over brighter desert areas. For further details on the C61 L1B changes and minor updates to other land products, users are requested to refer to this C61 Land change document. Additional details regarding the revision to the C61 L2 LSR high-aerosol flagging can be found here.

Users are requested to make a note of this proposed change in LANCE NRT MODIS products. For performance comparison of the C61 NRT and STD products, users can still refer to the C6 performance metrics that can be found that can be found here.

If you have any further concern or question about this transition, please contact the LANCE MODIS User Support and for questions or information related to change in product quality contact land QA team.

• 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 1 April 2021, at which time, only C6.1 NRT products will be available.

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.