MOD16A2 Unit Conversion

[subhadip_007]

I need ET in m/8d or mm/8d. How to convert MOD16A2 kg/m²/8day to one of my units? Please help me with this. Or any other dataset I can use with my unit.

[LP DAACx - lien]

Hi,
Sorry for the delay, we wanted to confirm with the developer of the product.
"The kg/m2/8day units are equivalent to mm/8day. Therefore, you just need to apply the 0.1 scale factor to get ET in the desired mm/8day units as noted below. As a check, the typical ET rate over a humid temperate grassland in summer would be ~1-4 mm/day."
Thanks,
Brett

[valeria_22]

Hello
I need ET in mm/day. how to convert MOD16A2 kg/m²/8 day to one of my units?

[LP DAACx - dgolon]

Hi @valeria_22 ,

Above we listed the answer for mm/8 day, so you would just need to divide by 8 to get mm/day. However, if you are interested in ~daily data you might be interested in ECOSTRESS ET data which can be found here: https://lpdaac.usgs.gov/product_search/?query=ecostress&keyword=Evapotranspiration+%28ET%29&status=Operational&view=cards&sort=title

[linzeearth]

Hi@LP DAAC - dgolon,

I am so confuse about the unit mm/8 day, does it mean a average number of 8 day?
and how can i calculate the evaporation over a year with that unit?

thank you

LP DAAC - dgolon wrote:
> Hi @valeria_22 ,
>
> Above we listed the answer for mm/8 day, so you would just need to divide
> by 8 to get mm/day. However, if you are interested in ~daily data you might
> be interested in ECOSTRESS ET data which can be found here:
> https://lpdaac.usgs.gov/product_search/?query=ecostress&keyword=Evapotranspiration+%28ET%29&status=Operational&view=cards&sort=title

[LP DAACx - dgolon]

Hi @linzeearth The pixel values for the two Evapotranspiration layers (ET and PET) are the sum of all eight days within the composite period and the pixel values for the two Latent Heat layers (LE and PLE) are the average of all eight days within the composite period. Note that the last acquisition period of each year is a 5 or 6-day composite period, depending on the year.

You could average the data out to yearly but you will have some error you would need to identify. Instead, we recommend using the yearly product: https://doi.org/10.5067/MODIS/MOD16A3GF.061 You might also be interested in the Daily MODIS ET SSEBop Evapotranspiration data product. More information on that can be found here: https://earlywarning.usgs.gov/ssebop/modis/daily Thank you

[schsu]

Hi,

I have downloaded the 8-day evapotranspiration data (MOD16A2GF.061_ET_500m_doy2005XXX_aid0001.tif) from the online tool AppEEARS (https://appeears.earthdatacloud.nasa.gov). The tif files were generated according to the shapefile I uploaded.

Based on the previous reply and the user guide, the raw values in the data (integer) should be multiplied by the scale factor 0.1 to be the real value. However, I found in the tif files the values are already not integers. Also, the statistical analysis presented in the AppEEARS download section also uses (kg/m2/8day) as unit for ET_500m.

Therefore, I am wondering if the multiplication of the scale factor is already processed during the generation of tif files from AppEEARS. In other words, is it true that the MOD16A2 products downloaded from AppEEARS do not need to consider the scale factor?

Thank you in advance for your reply.

[LP DAACx - lien]

Hello,
The values in the .csv file are already scaled. However, the geotiff files are not supposed to be scaled.
Thanks,
Brett

[fredhensley]

Hi all,
Can you advise with converting to imperial units?
I still do it manually: https://oneconvert.com/unit-converters/length-converter/mm-to-inches
Thanks in advance.

[LP DAACx - lien]

Hello,
We typically work in metric but I'll see if anyone on our staff knows an easy way to convert. In the meantime, if anyone in the science community works in imperial we'll leave it open for you to share what you do. It does appear that the .csv file allows formulas to be entered for specific columns, so there should be a way.