MODIS Land News
Terra Orbital Drift Information
Terra is scheduled to exit the 'Morning Constellation' of Earth Science satellites by October, 2022. Because of onboard fuel shortage, the last of Terra mission maneuver was done on February 27, 2020 to maintain the mean local time (MLT) of 10:30 AM. Thereafter, Terra has been drifting slowly from its MLT and will reach and exceed 10:15 AM MLT by October 2022, when it will make the constellation exit with a lowered orbit altitude of 694kms. Terra MODIS will remain operational and generate the full suite of products until the end of the mission in December 2025.
More information can be found on the Terra website's orbital drift pages.
Similarly, the Aqua flight operations team completed the final 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 began its constellation exit; it exceeded a 1:45 PM MLT crossing in February 2023. MLT will continue to drift, 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.
Other Orbital Drift Resources
- Terra's Lower Orbit Virtual Community Forum
- Orbit Lowering Impacts on MODIS (Audio recording, Land portion begins at 10:30 min)
- View/download the slide deck associated with the above recording (MODIS slides 54-75, Land discipiline slides begin on slide 65)
MODIS Collection News
Decommissioning of the MODIS C6 Forward Processing (01/26/2023)
C6 Forward processing of Terra and Aqua MODIS Land data products will be discontinued, on or around mid-February 2023 (02/15/2023). The C6 land data products have always suffered from known calibration issues that were discovered by the instrument Cal/Val team after the completion of the C6 reprocessing. The main among these being the increased impact of optical crosstalk in the Terra PV LWIR bands 27-30, that had made retrieval of most atmospheric parameters infeasible, indirectly impacting some of the land products that were dependent on these atmospheric retrievals. The Collection 6.1 (C61) corrects for this and some other critical calibration issues and also has a number of product specific improvements and enhancements that are listed in the C61 change document here.
Given the improved performance and calibration of C61, users are requested to switch to C61 for all of their MODIS land data needs. DAACs, will retain the C6 historical land data products for a further period of 6 months, following this decommissioning of the C6 forward processing, and will decommission all C6 land data products after the expiry of this 6-month retention period.
MODIS C6.1
C61 reprocessing of Land products, with minor changes to the land algorithms using the C6.1 L1B as input, began in February 2020 with the exception of the MAIAC, VCF, Land cover and Phenology products. MODAPS is currently testing the MAIAC algorithm and is integrating code for the Land Cover and Phenology products. MODAPS is still awaiting delivery of the VCF algorithm.
Public release of C6.1 products began in Febuary 2021 and the plan is to complete reprocessing the entire archive by the end of 2021.
Note: The C6 Terra MODIS products, particularly the cloud products, were negatively impacted by optical crosstalk in the infrared bands (B27 – B30). Though the crosstalk issue was present from the beginning of the mission, its impact on the products were not significant until after year-2009, and became even more so following the MODIS Terra safe-hold in February of 2016. The C6.1 reprocessing implemented an approach to correct this crosstalk issue in the calibration from the beginning of the mission.
MODIS C7
Collection 7 L1B changes to calibration have been delivered by MCST. The calibration testing with downstream products has been completed.
After the evaluation of the L1B calibration testing by the discipline teams, operational C7 geolocation and L1B processing is planned for early 2025. The atmosphere and land products will not begin C7 reprocessing until mid to late 2025.
C7 reprocessing will use an annual Land/Water Mask (LWM). This new LWM will be incorporated into the geolocation product.
All the products in this collection will be in netCDF4 format.
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