Evaluation Summary of Mandiva Chain Test
The L1B and the downstream Land and Atmosphere products from the MODAPS system may be created on computers running any one of three different operating systems: Irix, Mandrake Linux, and Mandriva Linux (2008). The Irix and the Mandriva (2008) products are nearly identical, but the Mandrake products differ in a small percentage of the pixels. The reason for this is that the compilers for these three operating systems each have slightly different implementations for floating point operations. As a result, the floating point numbers come out slightly different on each platform.
However most of the MODIS L1B and downstream L2/L3/L4 land and atmosphere products are not stored as floating point values, but as scaled integer (SI) values with a floating point scale and offset. When converted to an integer, a very small difference in a floating point value can, in a small number of cases, cause the resulting integer to be rounded either to a higher or a lower integer, causing a larger difference in the integer values. In addition to the difference caused by the floating point operation, minor differences introduced in the L1B output, often as small as 1 count, could be slightly amplified by the downstream land and atmosphere PGEs by certain non-linear operations involving fixed threshold. However overall the differences are negligible and happen to very small percentage of global data and hence should not be of any concern.
MODAPS recently ran a 32-day chain test of all the land PGEs on two processing systems with different operating systems: mandrake and the mandriva-2008. Following table contains percentage of global retrievals with a relative absolute difference of 1% (relative to the values retrieved by mandrake) or less in values between the products produced from these two platforms. This analysis confirms that the number of pixels affected is very small and the difference is within the calibration error. Please note that since a difference of 1 or 2 counts in data values is generally present at most pixels, and so an absolute difference of 2 or less at any pixel is truncated to zero. The global browse images of the land products from the two processing systems are available at L630 test browse page.
Mandriva test results - Daily products
All daily product results are from 1 day worth of global data, from day 2005042.
| ESDT | SDS Name | Result Summary |
|---|
| MOD09 |
250m Band 1 reflectance |
99.9999% within 1% (less than 50,000 out of approximately 6 billion pixels has difference >1%.) |
|---|
| 250m Band 2 reflectance |
99.9999% within 1% (less than 80,000 out of approximately 6 billion pixels has difference >1%.) |
| 500m Band 3 reflectance |
99.9999% within 1% (about 25,000 out of approximately 1.7 billion pixels has difference >1%.) |
| 500m Band 4 reflectance |
99.9999% within 1% (about 25,000 out of approximately 1.7 billion pixels has difference >1%.) |
| 500m Band 5 reflectance |
99.9999% within 1% (about 17,000 out of approximately 1.7 billion pixels has difference >1%.) |
| 500m Band 6 reflectance |
99.9999% within 1% (less than 4,000 out of approximately 1.7 billion pixels has difference >1%.) |
| 500m Band 7 reflectance |
99.9999% within 1% (less than 4,000 out of approximately 1.7 billion pixels has difference >1%.) |
| MOD09CMG |
Band 1 CMG reflectance |
99.9999% within 1% (about 1,000 out of approximately 26 million pixels has difference >1%.) |
|---|
| Band 2 CMG reflectance |
99.9999% within 1% (about 1,000 out of approximately 26 million pixels has difference >1%.) |
| Band 3 CMG reflectance |
99.9999% within 1% (about 1,100 out of approximately 26 million pixels has difference >1%.) |
| Band 4 CMG reflectance |
99.9999% within 1% (about 1,100 out of approximately 26 million pixels has difference >1%.) |
| Band 5 CMG reflectance |
99.9999% within 1% (about 850 out of approximately 26 million pixels has difference >1%.) |
| Band 6 CMG reflectance |
99.9999% within 1% (about 175 out of approximately 26 million pixels has difference >1%.) |
| Band 7 CMG reflectance |
99.9999% within 1% (about 185 out of approximately 26 million pixels has difference >1%.) |
| MOD10A1 |
Snow_Cover_Daily_Tile |
100% of data were within 1% |
|---|
| Snow_Albedo_Daily_Tile |
100% of data were within 1% |
| Fractional_Snow_Cover |
100% of data were within 1% |
| MOD11 |
LST |
99.9999% within 1% (less than 30 out of 780 million + pixels has difference >1%.) |
|---|
| Emis_31 |
99.9999% within 1% (less than 15,000 out of 780 million + pixels has difference >1%.) |
| Emis_32 |
99.9999% within 1% (less than 15,000 out of 780 million + pixels has difference >1%.) |
| MOD15A1 |
1km FPAR |
99.9999% within 1% (about 2500 out of about 400 million pixels has difference >1%.) |
|---|
| 1km LAI |
99.9999% within 1% (about 375 out of approximately 26 million pixels has difference >1%.) |
| MOD29 |
Sea Ice by reflectance |
99.9999% match (less than 300 out of approximately 275 million pixels do not match) |
|---|
| Ice surface temperature |
100% of data were within 1% |
| MOD29E1D |
Sea Ice by reflectance - NP |
99.9999% match (less than 100 out of approximately 20 million pixels do not match) |
|---|
| Sea Ice by reflectance - SP |
99.9999% match (less than 10 out of approximately 20 million pixels do not match) |
| Ice surface temperature - NP |
100% of data were within 1% |
| Ice surface temperature - SP |
100% of data were within 1% |
Mandriva test results - n-day products
Day 2005033
| ESDT | SDS Name | Result Summary |
|---|
| MOD09A1 |
Band 1 reflectance |
99.9999% within 1% (about 110,000 out of approximately 1.7 billion pixels has difference >1%.) |
|---|
| Band 2 reflectance |
99.9999% within 1% (less than 93,000 out of approximately 1.7 billion pixels has difference >1%.) |
| Band 3 reflectance |
99.9999% within 1% (about 135,000 out of approximately 1.7 billion pixels has difference >1%.) |
| Band 4 reflectance |
99.9999% within 1% (about 150,000 out of approximately 1.7 billion pixels has difference >1%.) |
| Band 5 reflectance |
99.9999% within 1% (about 86,000 out of approximately 1.7 billion pixels has difference >1%.) |
| Band 6 reflectance |
99.9999% within 1% (less than 44,000 out of approximately 1.7 billion pixels has difference >1%.) |
| Band 7 reflectance |
99.9999% within 1% (less than 44,000 out of approximately 1.7 billion pixels has difference >1%.) |
| MOD10A2 |
Maximum snow extent |
99.9999% of pixels match (about 27,000 out of approximately 1.7 billion pixels do not match.) |
|---|
| MOD11A2
| LST 1km Day |
99.9999% within 1% (about 2,400 out of approximately 456 million pixels has difference >1%.) |
|---|
| LST 1km night |
99.9999% within 1% (about 5,400 out of approximately 456 million pixels has difference >1%.) |
| MOD13A1 |
NDVI |
99.9999% within 1% (about 52,000 out of approximately 1.7 billion pixels has difference >1%.) |
|---|
| EVI |
99.9999% within 1% (less than 100,000 out of approximately 1.7 billion pixels has difference >1%.) |
| MOD13A2 |
NDVI |
99.9997% within 1% (less than 100,000 out of approximately 420 million pixels has difference >1%.) |
|---|
| EVI |
99.9998% within 1% (about 70,000 out of approximately 420 million pixels has difference >1%.) |
| MOD14A2 |
Fire Mask |
99.9999% of pixels match (about 30 out of approximately 410 million pixels do not match.) |
|---|
| MOD15A2 |
FPAR |
99.9999% within 1% (less than 6,700 out of approximately 410 million pixels has difference >1%.) |
|---|
| LAI |
99.9999% within 1% (less than 2,200 out of approximately 410 million pixels has difference >1%.) |
| MOD17A2 |
GPP |
99.9998% within 1% (less than 60,000 out of approximately 410 million pixels has difference >1%.) |
|---|
| PSNNet |
99.9998% within 1% (less than 60,000 out of approximately 410 million pixels has difference >1%.) |
For details on test and evaluation please contact Sadashiva Devadiga .
