MODIS Overview

The NSIDC DAAC MODIS data collection includes a suite of snow cover and sea ice data sets derived from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard both the Aqua and Terra satellites.

MODIS is the first NASA mission to provide daily global coverage at moderate resolution (250 meters). Because MODIS sensors have operated successfully since the Terra and Aqua satellites launched, MODIS data provide a continuous, consistent observation record dating back to the year 2000. 

As the Aqua and Terra satellites orbit the earth, their MODIS instruments collect imagery of the same area on Earth approximately three hours apart. The entire Earth's surface is imaged every one to two days, and the sensors work in tandem to optimize cloud-free surface viewing. Because they have polar orbits, the sensors view high latitudes and polar regions multiple times each day.

In multiple ways, MODIS data sets at NSIDC facilitate a better understanding of how the cryosphere has influenced our planet over time:

  • These sensors provide opportunities to investigate processes occurring on sub-daily time scales.
  • The uninterrupted 20+-year MODIS record captures the seasonal evolution of snow and ice cover year after year. This record enables comparisons between years, over a period of rapid environmental change.
  • Snow and ice reflect most of the sunlight reaching them back into space, so MODIS snow and sea ice can be used to study Earth’s energy balance.
  • MODIS data can feed climate models, whether they are related to the polar regions or the entire globe.

MODIS data sets available from NSIDC have been used to study a wide range of topics including glacier surface elevation, Tibetan lake ice extent, Alaskan permafrost change, even Iberian wolf pack size.

Terra versus Aqua MODIS products

Because MODIS sensors have flown on both the Terra and Aqua satellites, NSIDC offers parallel  products derived from MODIS on each satellite. Terra and Aqua products are very similar with a few key differences:

  • Terra launched two years before Aqua, so the Terra record starts earlier, with observations beginning in 2000.
  • Due to Band 6 detector failures on Aqua shortly after launch, Version 5 and earlier snow products from MODIS Aqua were produced differently than their Terra counterparts. This made comparing the output from the two collections harder. In 2012, researchers resolved this problem by developing a post processing technique to restore Aqua Band 6 data to scientific quality. This technique was incorporated into NSIDC products starting in 2015, with the publication of Version 6. Detailed information is available from the MODIS data versions page.
  • Terra crosses the equator from north to south at roughly 10:30 a.m. local time. Aqua crosses the equator from south to north at roughly 1:30 p.m. local time.

More detail on data capture is provided in MODIS technical references and in user guides for each product.

Ongoing changes in Terra and Aqua orbits
The Terra flight operations team conducted Terra’s last inclination adjust maneuver to maintain Terra’s orbit in February 2020. The inclination adjust maneuvers were used to control the platform’s 10:30 AM mean local time (MLT) equator crossing. Terra will continue to drift and is expected to reach a 10:15 AM MLT in October 2022. At that time, the flight operations team will have Terra exit the Earth Sciences Constellation and lower Terra to an altitude of 694 km by performing two retrograde maneuvers. MLT will continue to drift after these maneuvers, reaching 9:00 AM around December 2025. Terra MODIS will remain operational and generate the full suite of products until the end of the mission in December 2025.
Similarly, the Aqua flight operations team completed mission manuevers related to maintaining a 1:30 PM MLT equator crossing and 705 km orbit altitude on March 18, 2021. In July 2021, Aqua began drifting to a later MLT. In January 2022, Aqua will begin its constellation exit by stopping all maneuvers except collision avoidance maneuvers and will exceed a 1:45 PM MLT crossing in February 2023. MLT will continue to drift after this, reaching 3:50 PM around August 2026. Aqua MODIS will remain operational and generate the full suite of products until the end of the mission in August 2026.
Earlier (later) crossing times for a morning (afternoon) platform like Terra (Aqua) mean lower solar elevations leading to more prevalent shadows. This decrease in orbit altitude alters the spatial coverage of the sensor including possible gaps in spatial sampling, decreased spatial coverage, and higher spatial resolution. Products are mostly expected to be science quality except for reduced grid size (from lower altitude) and without a strict 16-day repeat of observations (from drift and changing orbit).
Details on the impact of the Constellation Exit on the quality of the product are being compiled and will be posted when available.

Parameters

Snow cover, snow extent, albedo, sea ice extent, sea ice temperature

Geographic coverage

Global

Sensor(s) and satellite(s)

MODIS is a 36-channel visible to thermal-infrared sensor that provides global coverage on polar-orbiting satellites. MODIS flies on the Terra satellite (launched 18 December 1999) and the Aqua satellite (launched 4 May 2002)

Related collection(s) 

VIIRS

Explore Images from MODIS

MODIS