MYD21C2 v061

MODIS/Aqua Land Surface Temperature/3-Band Emissivity 8-Day L3 Global 0.05 Deg CMG


PI: Glynn C. Hulley

Historic processing continues for MODIS V6.1 data products for years 2011 through 2018. It is the intent to complete processing of the archive by the end of the 2021 calendar year.

Description

A new suite of Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature and Emissivity (LST&E) products are available in Collection 6.1. The MYD21 Land Surface Temperature (LST) algorithm differs from the algorithm of the MYD11 LST products, in that the MYD21 algorithm is based on the ASTER Temperature/Emissivity Separation (TES) technique, whereas the MYD11 uses the split-window technique. The MYD21 TES algorithm uses a physics-based algorithm to dynamically retrieve both the LST and spectral emissivity simultaneously from the MODIS thermal infrared bands 29, 31, and 32. The TES algorithm is combined with an improved Water Vapor Scaling (WVS) atmospheric correction scheme to stabilize the retrieval during very warm and humid conditions.

The MYD21C2 dataset is an 8-day composite LST product that uses an algorithm based on a simple averaging method. The algorithm calculates the average from all the cloud free MYD21A1D and MYD21A1N daily acquisitions from the 8-day period. Unlike the MOD21A1 data sets where the daytime and nighttime acquisitions are separate products, the MYD21A2 contains both daytime and nighttime acquisitions as separate Science Dataset (SDS) layers within a single Hierarchical Data Format (HDF) file. The LST, Quality Control (QC), view zenith angle, and viewing time have separate day and night SDS layers, while the values for the MODIS emissivity bands 29, 31, and 32 are the average of both the nighttime and daytime acquisitions. MYD21C2 products are available two months after acquisition due to latency of data inputs. Additional details regarding the method used to create this Level 3 (L3) product are available in the Algorithm Theoretical Basis Document (ATBD).

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Characteristics

Improvements/Changes from Previous Versions

  • The Version 6.1 Level-1B (L1B) products have been improved by undergoing various calibration changes that include: changes to the response-versus-scan angle (RVS) approach that affects reflectance bands for Aqua and Terra MODIS, corrections to adjust for the optical crosstalk in Terra MODIS infrared (IR) bands, and corrections to the Terra MODIS forward look-up table (LUT) update for the period 2012 - 2017.
  • A polarization correction has been applied to the L1B Reflective Solar Bands (RSB).
  • Three new CMG products are available in the MxD21 suite (MxD21C1/C2/C3).

Product Maturity

Validation at stage 1 has been achieved for the MODIS Land Surface Temperature and Emissivity data products. Further details regarding MODIS land product validation for the MYD21 data products are available from the MODIS Land Team Validation site.

Collection and Granule

Collection

Characteristic Description
CollectionAqua MODIS
DOI10.5067/MODIS/MYD21C2.061
File Size~110 MB
Temporal ResolutionMulti-Day
Temporal Extent2002-07-04 to Present
Spatial ExtentGlobal
Coordinate SystemGeographic Latitude and Longitude
DatumN/A
File FormatHDF-EOS
Geographic DimensionsGlobal

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers27
Columns/Rows7200 x 3600
Pixel Size5600 m

Layers

SDS Name Description Units Data Type Fill Value No Data Value Valid Range Scale Factor Additional Offset
Count_Day Count of Daytime Input Values N/A 16-bit unsigned integer 0 N/A 1 to 65535 N/A N/A
Count_Night Count of Nighttime Input Values N/A 16-bit unsigned integer 0 N/A 1 to 65535 N/A N/A
QC_Day Quality Control for Daytime LST and Emissivity N/A 8-bit unsigned integer N/A N/A 0 to 255 N/A N/A
QC_Night Quality Control for Nighttime LST and Emissivity N/A 8-bit unsigned integer N/A N/A 0 to 255 N/A N/A
LST_Day Average Daytime Land Surface Temperature Kelvin 16-bit unsigned integer 0 N/A 7500 to 65535 0.02 N/A
LST_Night Average Nighttime Land Surface Temperature Kelvin 16-bit unsigned integer 0 N/A 7500 to 65535 0.02 N/A
LST_Day_err Root-mean-square-error Daytime Land Surface Temperature Kelvin 8-bit unsigned integer 0 N/A 1 to 255 0.04 N/A
LST_Night_err Root-mean-square-error Nighttime Land Surface Temperature Kelvin 8-bit unsigned integer 0 N/A 1 to 255 0.04 N/A
Day_view_angle Average Daytime View Zenith Angle Degree 8-bit unsigned integer 255 N/A 0 to 130 N/A -65
Night_view_angle Average Nighttime View Zenith Angle Degree 8-bit unsigned integer 255 N/A 0 to 130 N/A -65
Day_view_time Average Daytime View Time (UTC) Hours 8-bit unsigned integer 255 N/A 0 to 120 0.2 N/A
Night_view_time Average Nighttime View Time (UTC) Hours 8-bit unsigned integer 255 N/A 0 to 120 0.2 N/A
Emis_29_Day Average Daytime Band 29 Emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_29_Night Average Nighttime Band 29 Emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_29_Day_err Root-mean-square-error Daytime Band 29 Emissivity N/A 16-bit unsigned integer 0 N/A 1 to 65535 0.0001 N/A
Emis_29_Night_err Root-mean-square-error Nighttime Band 29 Emissivity N/A 16-bit unsigned integer 0 N/A 1 to 65535 0.0001 N/A
Emis_31_Day Average Daytime Band 31 Emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_31_Night Average Nighttime Band 31 Emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_31_Day_err Root-mean-square-error Daytime Band 31 Emissivity N/A 16-bit unsigned integer 0 N/A 1 to 65535 0.0001 N/A
Emis_31_Night_err Root-mean-square-error Nighttime Band 31 Emissivity N/A 16-bit unsigned integer 0 N/A 1 to 65535 0.0001 N/A
Emis_32_Day Average Daytime Band 32 Emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_32_Night Average Nighttime Band 32 Emissivity N/A 8-bit unsigned integer 0 N/A 1 to 255 0.002 0.49
Emis_32_Day_err Root-mean-square-error Daytime Band 32 Emissivity N/A 16-bit unsigned integer 0 N/A 1 to 65535 0.0001 N/A
Emis_32_Night_err Root-mean-square-error Nighttime Band 32 Emissivity N/A 16-bit unsigned integer 0 N/A 1 to 65535 0.0001 N/A
Percent_land_in_grid Percent of Land Detections in Grid Cell Percent 8-bit unsigned integer 255 N/A 1 to 100 N/A N/A
Clear_sky_days Bitmap of Clear Sky Days (1 = clear, LSB = 1st day) N/A 8-bit unsigned integer N/A N/A 0 to 255 N/A N/A
Clear_sky_nights Bitmap of Clear Sky Nights (1 = clear, LSB = 1st day) N/A 8-bit unsigned integer N/A N/A 0 to 255 N/A N/A

Product Quality

The QC layer is stored in an efficient bit-encoded manner. The unpack_sds_bits executable from the LDOPE Tools is available to the user community to help parse and interpret the quality layer.

The final quality bit for the output product reflects the lowest quality values from all observations that went into the final average. The bit definition index for the QC layer is available in Table 12 of the User Guide.

Known Issues

Users of MODIS LST products may notice an increase in occurrences of extreme high temperature outliers in the unfiltered MxD21 Version 6 and 6.1 products compared to the heritage MxD11 LST products. This can occur especially over desert regions like the Sahara where undetected cloud and dust can negatively impact both the MxD21 and MxD11 retrieval algorithms.

In the MxD11 LST products, these contaminated pixels are flagged in the algorithm and set to fill values in the output products based on differences in the band 32 and band 31 radiances used in the generalized split window algorithm. In the MxD21 LST products, values for the contaminated pixels are retained in the output products (and may result in overestimated temperatures), and users need to apply Quality Control (QC) filtering and other error analyses for filtering out bad values. High temperature outlier thresholds are not employed in MxD21 since it would potentially remove naturally occurring hot surface targets such as fires and lava flows.

High atmospheric aerosol optical depth (AOD) caused by vast dust outbreaks in the Sahara and other deserts highlighted in the example documentation are the primary reason for high outlier surface temperature values (and corresponding low emissivity values) in the MxD21 LST products. Future versions of the MxD21 product will include a dust flag from the MODIS aerosol product and/or brightness temperature look up tables to filter out contaminated dust pixels. It should be noted that in the MxD11B day/night algorithm products, more advanced cloud filtering is employed in the multi-day products based on a temporal analysis of historical LST over cloudy areas. This may result in more stringent filtering of dust contaminated pixels in these products.

In order to mitigate the impact of dust in the MxD21 V6 and 6.1 products, the science team recommends using a combination of the existing QC bits, emissivity values, and estimated product errors, to confidently remove bad pixels from analysis. For more details, refer to this dust and cloud contamination example documentation.

For complete information about known issues please refer to the MODIS/VIIRS Land Quality Assessment website.


About the image

A global image of the Aqua MODIS land surface temperature (LST) data product from MYD21C2 January 17 - 24, 2021.

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Documentation

User Guide
Algorithm Theoretical Basis Document (ATBD)
File Specification

Using the Data

Access Data

Citation

DOI: 10.5067/MODIS/MYD21C2.061