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MODIS/Aqua Sea Ice Extent Daily L3 Global 1km EASE-Grid Day (MYD29P1D) contains the following fields: sea ice by reflectance, sea ice by reflectance spatial quality assurance (QA), ice surface temperature (IST), IST spatial QA, sea ice by IST, and combined sea ice in HDF-EOS format along with corresponding metadata. Data are available from 04 July 2002 to 03 January 2007. The sea ice algorithm uses a Normalized Difference Snow Index (NDSI) modified for sea ice to distinguish sea ice from open ocean based on reflective and thermal characteristics. The only data available for Version 4 (V004) is the Golden Month, which is a sample of V004 data covering the time period 29 August 2002 (day of year 241) through 7 October 2002 (day of year 280). The Golden Month is only available by special request by contacting NSIDC User Services.
Please note that NSIDC now has a complete series of Version 5 data, which is the highest version number now available and represents the best quality of data.
As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.
The following example shows how to cite these data in a publication. List the principal investigators, year of data set release (2004), data set title and version, date of the version you used, publisher (NSIDC), and digital media.
Hall, D.K., G.A. Riggs, and V.V. Salomonson. 2001, updated daily. MODIS/Aqua Sea Ice Extent Daily L3 Global 1km EASE-Grid Day V004, December 2003 to March 2004. Boulder, CO, USA: National Snow and Ice Data Center. Digital media.
|Spatial coverage and resolution||
Coverage is global, but the sea ice algorithm applies only to ocean pixels. Gridded resolution is 1 km.
|Temporal coverage and resolution||
Data are available from 04 July 2002 to 03 January 2007. Temporal resolution is daily for MYD29P1D.
|Tools for accessing data|
Pixel values vary by field. See Parameter Range for details.
|Grid type and size||
MYD29P1D data are gridded to EASE-Grid tiles, 951 x 951 pixels in size.
|File naming convention||
Each data granule is 6.26 MB.
The sea ice algorithm classifies pixels as sea ice, cloud, open ocean, inland water, or land. The algorithm also calculates Ice Surface Temperature (IST) for each pixel.
|Procedures for obtaining data||
Contact NSIDC User Services to order data.
Dorothy K. Hall
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Vincent V. Salomonson
NASA Goddard Space Flight Center
Greenbelt, MD 20771
George A. Riggs
Science Systems and Applications, Inc. NASA Goddard Space Flight Center
Greenbelt, MD 20771
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
Algorithms that generate sea ice products are continually being improved, as limitations become apparent in early versions of data. As a new algorithm becomes available, a new version of data is released. Users are encouraged to work with the latest version available, which is the highest version number. Version 4 (V004) is the most current version of MYD29P1D data available. See MODIS Product Versions for the reprocessing history and summary of changes in each version.
Please visit the following sites for more information about known data problems, production schedule, and future plans:
MODIS products are archived in HDF-EOS format, which employs point, swath, and grid structures to geolocate parameters to geographic coordinates. Various software packages, including public domain software, support the HDF-EOS data format. See the Software section for more information.
Sea ice by reflectance with HDF-predefined and custom local attributes
Sea ice by reflectance spatial QA with HDF-predefined and custom local attributes
Ice surface temperature with HDF-predefined and custom local attributes.
Ice surface temperature spatial QA with HDF-predefined and custom local attributes
Sea ice by ice surface temperature with HDF-predefined and custom local attributes
All MYD29P1D products contain the same global attributes.
Sea Ice by Reflectance
The sea ice algorithm identifies pixels as being sea ice, ocean, cloud, land, inland water, or other condition. Sea ice is distinguished from open water based on reflective properties. Results are stored as integer values.
Ice Surface Temperature
IST data are expressed in Kelvins and are stored as scaled integer data in HDF-EOS calibrated form. You must convert data to Kelvins using the calibration data in the HDF predefined local attributes:
IST = 0.01 * (calibrated data - add_offset)
The valid range for IST is 243 to 271.5 K.
Sea Ice by Reflectance SpatialQA and Ice Surface Temperature SpatialQA
These fields store the quality of the algorithm on a pixel-by-pixel basis. QA information tells if the algorithm results were nominal, abnormal, cloud-obscured, invalid, or if other defined conditions were encountered for a pixel. If all the input data and calculations in the algorithm were nominal for a pixel, the QA bit is set to nominal. If data showed abnormal values, for example out of range, the algorithm proceeds and outputs a value but flags it as abnormal. If the pixel is obscured by cloud, then the bit setting is cloud. If invalid data or calculations result in unacceptable values, the bit setting is invalid. See MODIS Sea Ice Quality Assurance Fields for more information about QA flags in sea ice products.
Sea Ice by IST
A pixel with an IST less than or equal to 271.5 K is classified as sea ice, and any pixel above that threshold is classified as open ocean.
Combined Sea Ice
This field represents the agreement or disagreement between sea ice identified by reflectance characteristics or by estimated IST. Data show pixels that were detected as sea ice in both the Sea Ice by Reflectance and Sea Ice by IST fields, and where the two techniques differed in detection of sea ice. Presence of other features, such as land, is consistent between these two fields.
A separate ASCII text file containing metadata with a .met file extension accompanies the HDF-EOS file. The metadata file contains some of the same metadata as in the product file, but also includes other information regarding archiving, user support, and post production quality assurance (QA) relative to the granule ordered. The post-production QA metadata may or may not be present depending on whether or not the data granule has been investigated for quality assurance. The metadata file should be examined to determine if post-production QA has been applied to the granule (Riggs, Hall, and Salomonson 2003).
MYD = MODIS/Aqua
2003 = Year of data acquisition (2003) 140 = Julian date of data acquisition (day 141)
h03 = horizontal tile number (3)
v08 = vertical tile number (8)
004 = Version number
2003 = Year of production (2003)
143 = Julian date of production (day 143)
023523 = Hour/minute/second of production in GMT (02:35:23)
Each data granule is 6.26 MB.
Coverage is global; however, only ocean granules are produced. The following resources can help you select and work with MYD29P1D tiles:
The following maps show tile locations for MYD29P1D. Click on the thumbnail images to see the full resolution images.
See the following for bounding coordinates of each tile:
MODIS Sea Ice Tile Bounding Coordinates, Northern Hemisphere
MODIS Sea Ice Tile Bounding Coordinates, Southern Hemisphere
MODLAND Tile Calculator: converts between MODIS tile numbers and latitude/longitude coordinates.
MODIS coverage is global; however, only ocean granules are used to create sea ice products. Gridded resolution is 1 km.
MYD29P1D data are gridded to the NSIDC EASE-Grid, a Lambert Azimuthal Equal Area projection. Please review All About EASE-Grid for general information on the EASE-Grid.
MYD29P1D data are gridded to Polar EASE-Grid tiles, each 951 x 951 pixels in size, which corresponds to approximately 954 km by 954 km at a resolution of 1002.7010 m per pixel.
Data extend from 04 July 2002 to 03 January 2007.
Temporal resolution is daily for MYD29P1D.
The sea ice algorithm classifies pixels as sea ice, cloud, open ocean, inland water, or land. In the Sea Ice by Reflectance field, sea ice is distinguished from open water based on reflective properties. Sea ice extent is determined by the number of pixels classified as sea ice. In the IST field, pixels classified as sea ice contain an IST value in Kelvins, and pixel values are scaled by 100 for all classes. The IST algorithm was designed for sea ice; however, IST values are provided for areas over open ocean.
Sea Ice by Reflectance and Sea ice by IST:
1: No decision
37: Lake or inland water
39: Open water (ocean)
50: Cloud obscured
200: Sea ice
Combined Sea Ice:
1: No decision
37: Lake or inland water
39: Open water (ocean)
50: Cloud obscured
150: Sea ice by IST only
170: Sea ice by reflectance only
237: Sea ice by both reflectance and IST
You must convert data to Kelvins using the calibration data in the HDF predefined local attributes:
IST = 0.01 * (calibrated data - add_offset)
1.0: No decision
37.0: Lake or inland water
39.0: Open water (ocean)
50.0: Cloud obscured
243.0 to 271.5: IST (Kelvins)
Because sea ice varies in concentration from near zero to 100 percent, it can show different reflectances and temperatures within a pixel, due to sub-pixel effects. Sea ice can also have different reflectances depending on snow cover and presence of surface melt monds. Melt ponds and leads in the summer months affect the emissivity of the ice surface; thus, also affecting the calculation of ice surface temperature. Clouds may obscure sea ice observations, which is a problem when noting the movement of sea ice over an eight-day time series. Small ice floes, polynyas, and leads at subpixel resolution also contribute to errors in identification and mapping of sea ice (Hall et al. 1998).
Accuracy of IST is estimated to be 0.3 to 2.1 Kelvins (Key et al. 1997). MODIS Airborne Simulator (MAS) data and campaign field data are currently used to establish bounds for MODIS IST accuracy.
The quality of MYDP1D daily sea ice maps is greatly improved in Version 4, since the quality was improved with input Version 4 MYD29 data. Validation status is set to provisional until further validation work specific to Aqua IST maps can be completed.
Analysis of the quality of the sea ice data products is an ongoing activity. Specific information on the science quality of the sea ice data products is reported in the ScienceQualityFlagExplanation object in the CoreMetadata.0 global attribute. The URL for the quality assessment site is given in the product metadata and is linked to from the Warehouse Inventory Search Tool (WIST) when ordering data. The ScienceQualityFlagExplanation is changed in response to analysis and should be checked for updated information. In the MOD29 and MOD29P1D data products there are two instances of the ScienceQualityFlagExplanation, one for sea ice determined by reflectance data and one for IST written in the metadata. Information on both is posted at that URL.
The Ice Surface Temperature PixelQA and the Sea Ice by Reflectance PixelQA data fields provide additional information on algorithm results for each pixel within a spatial context, and are used as a measure of usefulness for sea ice data. QA data are stored as bit flags. QA information is extracted by reading the bits within a byte (See MODIS Sea Ice Quality Assurance Fields). The QA information tells if algorithm results were nominal, abnormal, or if other defined conditions were encountered for a pixel (Riggs, Hall, and Salomonson 2003).
See MODIS Land Quality Assessment for further details.
Contact NSIDC User Services to order data.
The following sites can assist in selecting appropriate MODIS data for your study:
HDF-EOS to GeoTIFF converter (HEG): This free tool converts many HDF-EOS files to GeoTIFF, native binary, or HDF-EOS Grid. It also has reprojection, resampling, subsetting, stitching (mosaicing), and metadata creation capabilities.
Hierarchical Data Format - Earth Observing System (HDF-EOS): NSIDC provides more information about the HDF-EOS format, tools for extracting binary and ASCII objects from HDF, and a list of other HDF-EOS resources.
Sea ice is a highly dynamic feature that requires satellite-based remote sensing to better understand its behavior. Newly formed, smooth, thin sea ice is changed by temperature fluctuations, compressive and shear forces, surface currents, and winds. Sea ice usually becomes snow-covered only a few days after formation. As snow melts on sea ice, albedo decreases across all wavelengths. Sea ice has a much higher albedo compared to open ocean. Specific reflective characteristics of sea ice depend on the age of the ice. Snow-covered, opaque, white sea ice, thick first-year ice, and multiyear ice typically show maximum reflectance between 0.4 µm and 0.8 µm, and again at 1.9 µm. Young sea ice has a lower spectral albedo, 10-40 percent, than older sea ice when measured in this spectral range. Sea ice in the process of ablation and formation of melt ponds shows a decrease in reflectance from 0.6 µm to 0.8 µm, followed by a consistent decrease to approximately 1.6 µm. Sea ice reflectance criteria are used to identify snow-covered sea ice and the age of the ice (Hall and Martinec 1985, Hall et al. 1998).
Measurement of IST is useful for determining ice type and estimating radiative and turbulent heat fluxes for large-scale climate studies. IST estimates are used as an additional discriminatory variable for the identification of sea ice cover. Studies of MODIS Airborne Spectrometer (MAS) images in the Beaufort Sea, near St. Lawrence Island, Alaska, show that the surface temperature of water is typically greater than 271.4 Kelvins, while the surface temperature of saline ice is less than 271.4 Kelvins (Hall et al. 1998). These thresholds take into account the emissivity of sea ice. First-year ice has an emissivity of about 0.92, and multiyear ice has an emissivity of about 0.84. The difference in ice emissivities results in a difference in recorded surface temperatures, allowing a researcher to distinguish the relative age of ice and infer relative ice thickness (Hall and Martinec 1985).
The MODIS instrument provides 12-bit radiometric sensitivity in 36 spectral bands, ranging in wavelength from 0.4 µm to 14.4 µm. Two bands are imaged at a nominal resolution of 250 m at nadir, five bands at 500 m, and the remaining bands at 1000 m. A ±55° scanning pattern at 705 km achieves a 2330 km swath, with global coverage every one to two days.
The scan mirror assembly uses a continuously rotating double-sided scan mirror to scan ±55 degrees, driven by a motor encoder built to operate 100 percent of the time throughout the six year instrument design life. The optical system consists of a two-mirror off-axis afocal telescope which directs energy to four refractive objective assemblies: one each for the visible, near-infrared, shortwave-infrared, and longwave-infrared spectral regions (MODIS Web 2001).
|Orbit||1:30 p.m. ascending node (Aqua), sun-synchronous, near-polar, circular|
|Scan Rate||20.3 rmp, cross track|
|Swath Dimensions||2330 km (cross track) by 10 km (along track at nadir)|
|Telescope||17.78 cm diameter off-axis, afocal (collimated) with intermediate field stop|
|Size||1.0 x 1.6 x 1.0 m|
|Power||162.5 W (single orbit average)|
|Data Rate||10.6 Mbps (peak daytime); 6.1 Mbps (orbital average)|
|Spatial Resolution||250 m (bands 1-2)
500 m (bands 3-7)
1000 m (bands 8-36)
|Design Life||Six years|
|Primary Use||Band||Bandwidth||Spectral Radiance|
|Atmospheric Water Vapor||17||890-920 nm||10.0|
|Surface/Cloud Temperature||20||3.660-3.840 µm||0.45 (300 K)|
|21||3.929-3.989 µm||2.38 (335 K)|
|22||3.929-3.989 µm||0.67 (300 K)|
|23||4.020-4.080 µm||0.79 (300 K)|
|Atmospheric Temperature||24||4.433-4.498 µm||0.17 (250 K)|
|25||4.482-4.549 µm||0.59 (275 K)|
|27||6.535-6.895 µm||1.16 (240 K)|
|28||7.175-7.475 µm||2.18 (250 K)|
|Cloud Properties||29||8.400-8.700 µm||9.58 (300 K)|
|Ozone||30||9.580-9.880 µm||3.69 (250 K)|
|Surface/Cloud Temperature||31||10.780-11.280 µm||9.55 (300 K)|
|32||11.770-12.270 µm||8.94 (300 K)|
|Cloud Top Attitude||33||13.185-13.485 µm||4.52 (260 K)|
|34||13.485-13.785 µm||3.76 (250 K)|
|35||13.785-14.085 µm||3.11 (240 K)|
|36||14.085-14.385 µm||2.08 (220 K)|
The MODIS scan mirror assembly uses a continuously rotating double-sided scan mirror to scan ±55°, with a 20.3 rpm cross track. The viewing swath is 10 km along track at nadir, and 2330 km cross track at ±55°.
MODIS instruments were built to NASA specifications by Santa Barbara Remote Sensing, a division of Raytheon Electronics Systems.
MODIS has a series of on-board calibrators that provide radiometric, spectral, and spatial calibration of the MODIS instrument. The blackbody calibrator is the primary calibration source for thermal bands between 3.5 µm and 14.4 µm, while the Solar Diffuser (SD) provides a diffuse, solar-illuminated calibration source for visible, near-infrared, and shortwave infrared bands. The Solar Diffuser Stability Monitor (SDSM) tracks changes in the reflectance of the SD with reference to the sun so that potential instrument changes are not incorrectly attributed to changes in this calibration source. The Spectroradiometric Calibration Assembly (SRCA) provides additional spectral, radiometric, and spatial calibration.
MODIS uses the moon as an additional calibration technique and for tracking degradation of the SD, by referencing the illumination of the moon since the moon's brightness is approximately the same as that of the Earth. Finally, MODIS deep space views provide a photon input signal of zero, which is used as a point of reference for calibration (MODIS Web 2001).
The objective of the mission is to develop and implement algorithms that map snow and ice on a daily basis, and provide statistics of the extent and persistence of snow and ice over eight-day periods. Data at 500 m resolution enables sub-pixel snow mapping for use in regional and global climate models. A study of subgrid-scale snow-cover variability is expected to improve features of a model that simulates Earth radiation balance and land-surface hydrology (Hall et al. 1998).
A ±55° scanning pattern at 705 km achieves a 2330 km swath, with global coverage every one to two days.
The MODIS sensor contains a system whereby visible light from the earth passes through a scan aperture and into a scan cavity to a scan mirror. The double-sided scan mirror reflects incoming light onto an internal telescope, which in turn focuses the light onto four different detector assemblies. Before the light reaches the detector assemblies, it passes through beam splitters and spectral filters that divide the light into four broad wavelength ranges. Each time a photon strikes a detector assembly, an electron is created. Electrons are collected in a capacitor where they are eventually transferred into the preamplifier. Electrons are converted from an analog signal to digital data, and downlinked to ground receiving stations (MODIS Web 2001).
The EOS Ground System (EGS) consists of facilities, networks, and systems which archive, process, and distribute EOS and other NASA earth science data to the science and user community. The EOS Data and Operations System (EDOS) performs forward-link processing of data and return-link of science data from EOS spacecraft and instruments, processes telemetry to generate Level-0 products, and maintains a backup archive of Level-0 products.
EOSDIS ground stations are a component of EDOS, providing space to ground communication. EOSDIS ground stations comprise the Radio Frequency (RF) ground terminal, EDOS ground station interface, and the EOSDIS Backbone Network (EBnet) telecommunication system. The RF ground terminal provides space to ground link communication channels for receipt of science data, receipt of spacecraft telemetry data and transmission of spacecraft commands for two EOS spacecraft simultaneously, including X-band and S-band capabilities. The EDOS ground station interface monitors and captures the high-rate science data and transfers data to the EDOS Level-0 processing facility at the Goddard Space Flight Center (ESDIS 1996).
GSFC processes Level-1A data from Level-0 instrument packet data, then processes a Level-1B Calibrated Radiance product (MOD02) and Geolocation Fields (MOD03). The MODIS SIPS team creates a Level-2 product for sea ice (MOD29/MYD29), which is then used as input to create Level-3 gridded products for day and night sea ice data (MOD29P1D/MYD29P1D and MOD29P1N/MYD29P1N, respectively). These data are archived at the NSIDC DAAC and distributed to EOS investigators and other users via external networks and interfaces (MODIS Web 2000). Data are available to the public through the WIST.
The local equatorial crossing time of the Aqua satellite is approximately 1:30 p.m. in an ascending node with a sun-synchronous, near-polar, circular orbit.
Data products are generated by the MODIS Science Investigator-led Processing System (SIPS) and transferred to NSIDC. Figure 1 is a flowchart that summarizes the steps in the MODIS sea ice algorithm (Riggs, Hall, and Ackerman 1999), which identifies sea ice on the basis of reflectance characteristics in the visible and near infrared (IR) wavelengths, and also by IST. Algorithm criteria are based on the Normalized Difference Sea Ice Index (NDSI). The NDSI is used to detect the high reflectance of sea ice at visible wavelengths, and the low reflectance at approximately 1.6 µm. NDSI is calculated using MODIS bands 4 (0.55 µm) and 6 (1.6 µm) radiances:
NDSI = (band 4 - band 7)/(band 4 + band 7)
See the MODIS/Aqua Sea Ice Extent 5-Min L2 Swath 1km documentation for processing steps used in MYD29, the input to this data set.
The sea ice algorithm selects an observation of the day from multiple observations mapped to a MYD29G grid cell. A scoring algorithm selects the most favorable observation of the day based on
MYD29G-derived solar elevation, observation coverage in a grid cell, and distance from nadir. The objective is to select observations that are near nadir were acquired near noon local time, and have a large coverage area in a grid cell. This algorithm applies to daytime (reflectance) data. In day mode, MODIS collects both visible and thermal data. The scoring algorithm uses the visible data to determine the observation of the day for reflectance and thermal data. The thermal observation corresponding to the visible observation is the IST observation of the day (Riggs, Hall, and Salomonson 2003).
The sea ice algorithm classifies pixels as sea ice, cloud, open ocean, inland water, or land. Sea ice extent and IST are the primary variables of interest in this data set.
Hall, D.K., J.L. Foster, D.L. Verbyla, A.G. Klein, and C.S. Benson. 1998. Assessment of snow cover mapping accuracy in a variety of vegetation cover densities in central Alaska. Remote Sensing of the Environment 66: 129-137.
Hall, D.K., G.A. Riggs, and V.V. Salomonson. 1995. Development of methods for mapping global snow cover using Moderate Resolution Imaging Spectroradiometer (MODIS). Remote Sensing of the Environment 54(2): 127-140.
Hall, D.K., G.A. Riggs, and V.V. Salomonson. September 2001. Algorithm Theoretical Basis Document (ATBD) for the MODIS Snow-, Lake Ice- and Sea Ice-Mapping Algorithms. Greenbelt, MD: Goddard Space Flight Center. <http://modis-snow-ice.gsfc.nasa.gov/atbd.html> .
Markham, B.L. and J.L. Barker. 1986. Landsat MSS and TM post-calibration dynamic ranges, exoatmospheric reflectances and at-satellite temperatures. EOSAT Technical Notes 1:3-8.
MODIS Science and Instrument Team. MODIS Web. July 2003. <http://modis.gsfc.nasa.gov/> Accessed October 2000.
Riggs, G.A., D.K. Hall, and V.V. Salomonson. February 2003. MODIS sea ice products user guide. <http://modis-snow-ice.gsfc.nasa.gov/siugkc.html> .
Riggs, G.A., D.K. Hall, and S.A. Ackerman. 1999. Sea ice extent and classification mapping with the Moderate Resolution Imaging Spectroradiometer Airborne Simulator. Remote Sensing of the Environment 68: 152-163.
Wiscombe, W.J. and S.G. Warren. 1980. A model for the spectral albedo of snow I: pure snow. Journal of the Atmospheric Sciences 37: 2712-2733.
Please see the EOSDIS Glossary of Terms for a general list of terms.
Please see the EOSDIS Acronyms list for a general list of Acronyms. The following acronyms are used in this document:
ATBD: Algorithm Theoretical Basis Document
AVHRR: Advanced Very High Resolution Radiometer
EASE-Grid: Equal Area Scalable Earth Grid
EBNet: EOSDIS Backbone Network
ECS: EOSDIS Core System
EDOS: EOSDIS Data and Operations System
EGS: EOSDIS Ground System
EOS: Earth Observing System
EOSDIS: Earth Observing System Data and Information System
ERS: European Remote Sensing
ESDIS: Earth Science Data and Information System
ESDT: Earth Science Data Type
ftp: file transfer protocol
GMT: Greenwich Mean Time
GSFC: Goddard Space Flight Center
HDF-EOS: Hierarchical Data Format - Earth Observing System
IST: Ice Surface Temperature
MAS: MODIS Airborne Simulator
MCST: MODIS Characterization Support Team
MODIS: Moderate Resolution Imaging Spectroradiometer
MODLAND: MODIS Land
MSS: Multispectral Scanner
NASA: National Aeronautics and Space Administration
NCSA: National Center for Supercomputing Applications
NDSI: Normalized Difference Sea ice Index
NDVI: Normalized Difference Vegetation Index
NOAA: National Oceanic and Atmospheric Administration
NOHRSC: National Operational Hydrologic Remote Sensing Center
NSIDC: National Snow and Ice Data Center
PVL: Parameter Value Language
QA: Quality Assurance
RF: Radio Frequency
SAR: Synthetic Aperture Radar
SCF: Science Computing Facility
SD: Solar Diffuser
SDP: Science Data Processing
SDSM: Solar Diffuser Stability Monitor
SIPS: Science Investigator-led Processing System
SMMR: Scanning Multichannel Microwave Radiometer
SRCA: Spectroradiometric Calibration Assembly
SSM/I: Special Sensor Microwave/Imager
TM: Thematic Mapper