2.2. Landsat ARD Structure

Tile system

The global Landsat ARD product is provided as a set of 1x1 degree tiles. Tile names are derived from the tile center, and refer to their integer value of the tile center degrees. E.g., the name of a tile with center 17.5E and 52.5N is 017E_52N. Please use the shapefile glad_landsat_tiles.zip to select tiles for your area of interest.

 

16-day intervals

Each data granule (GeoTIFF file) contains observation data collected for a single 16-day interval. There are 23 intervals per year, see Table 2 (Landsat ARD Methodology) for interval dates. Each interval has a unique numeric ID, starting from the first interval of the year 1980. Use the 16-day interval ID table (16d_intervals.xlsx) to select intervals for your analysis.

 

Raster data

Each 16-day interval data stored as a single 8-band LZW-compressed GeoTIFF file in geographic coordinates (+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs), with the size of 4004x4004 pixels, an extent of 1.0005 by 1.0005 degrees, and a pixel size of 0.00025 degree. The tile system features a 2-pixel overlap to simplify parallelization of the focal average computation.

 

All raster layers are 16-bit unsigned. The list of layers are provided in Table 1 (see Landsat ARD Methodology for band wavelengths). The last layer (band 8) consists of a quality flag (QA) that reflects the quality of observation used to create the composite. Table 2 provides QA flag metadata. QA values 1, 15, and 2 are always considered as clear-sky observations. QA values 5 and 6 indicate seasonal quality issues (topographic shadows and snow cover). These observations may be removed from data processing if the number of clear-sky observations is sufficient. QA values 11-14 and 16-17 are considered as cloud-free data with an indication of potential cloud or cloud shadow contamination. QA values 15-17 are added to simplify intermittent water analysis (e.g., floods detection). QA values 3, 4, and 7-10 are considered contaminated by clouds and shadows and are usually excluded from data processing.

 

Table 1. 16-day composite image layers

Band number

Data

Units, Format

1

Normalized surface reflectance of blue band

Normalized surface reflectance scaled to the range from 1 to 40,000, UInt16

2

Normalized surface reflectance of green band

3

Normalized surface reflectance of red band

4

Normalized surface reflectance of NIR band

5

Normalized surface reflectance of SWIR1 band

6

Normalized surface reflectance of SWIR2 band

7

Normalized brightness temperature

degrees C * 100, UInt16

8

Observation quality code (QA). See 16d_intervals.xlsx for QA code description.

code, UInt16

 

Table 2. Per-pixel observation quality flag (QA)

QA code

Description

Quality

1

Land

clear-sky

2

Water

clear-sky

3

Cloud

Cloud contaminated

4

Cloud shadow

Shadow contaminated

5

Hillshade

clear-sky

6

Snow

clear-sky

7

Haze

Cloud contaminated

8

Cloud buffer

Cloud contaminated

9

Shadow buffer

Shadow contaminated

10

Shadow high likelihood

Shadow contaminated

11

Additional cloud buffer over land

clear-sky

12

Additional cloud buffer over water

clear-sky

14

Additional shadow buffer over land

clear-sky

15

Land, water detected but not used

clear-sky

16

Additional cloud buffer over land, water detected but not used

clear-sky

17

Additional shadow buffer over land, water detected but not used

clear-sky

 

Note for ARD v1.0 users:

The v1.0 16-day data was produced using the same methodology that the V1.1 data. The differences include the use of Landsat pre-collection data, incomplete coverage of Landsat 5 data (exclude recently added to the USGS archive), and different QA code (see below). The ARD v1.1 data is currently available east of 30W longitude. The data west of 30W longitude is only available in the v1.0 standard and is being reprocessed to the v1.1.

 

The QA flag is combined with the number of observations used to calculate the value for the 16-day interval. The output value is constructed as:

[QA ARD v1.0] = [Observation quality code * 100] + [number of observations]

In the v1.1 the number of observations is deprecated and the QA value consists of the observation quality code.