How to open HDF4 file with xarray

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Uchida Takaya

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Mar 10, 2016, 11:56:43 AM3/10/16

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To whom it may concern,

I am currently trying to read in a MODIS daily sea-surface temperature data in HDF4 format using xarray. A link to a sample data file is: ftp://podaac-ftp.jpl.nasa.gov/allData/modis/L3/aqua/11um/4km/daily/2003/001/A2003001.L3m_DAY_NSST_4.bz2

I have tried netCDF4 engine and pynio engine and none of them work. The codes that I have tried are:

fname = os.path.join('A2003001.L3m_DAY_NSST_4')

nc = xray.open_dataset(fname)

and the error I get is:

RuntimeError: NetCDF: Unknown file format

If I try using the netCDF4 engine as:

nc = xray.open_dataset(fname, engine='pynio')

I get the error:

NIOError: Unable to open file

Could you please show me how to get around this issue?

Sincerely,

Takaya Uchida

Stephan Hoyer

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Mar 12, 2016, 5:25:13 PM3/12/16

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Hi Takaya,

It looks like PyNIO (and hence xarray) can open this file if you rename it to have a ".h4" extension:

In [5]: mv /Users/Stephan/Downloads/A2003001.L3m_DAY_NSST_4/Users/Stephan/Downloads/A2003001.L3m_DAY_NSST_4.h4

In [6]: xr.open_dataset('/Users/Stephan/Downloads/A2003001.L3m_DAY_NSST_4.h4', engine='pynio')

Out[6]:

<xarray.Dataset>

Dimensions: (fakeDim0: 4320, fakeDim1: 8640, fakeDim2: 4320, fakeDim3: 8640)

Coordinates:

* fakeDim0 (fakeDim0) int64 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ...

* fakeDim1 (fakeDim1) int64 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ...

* fakeDim2 (fakeDim2) int64 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ...

* fakeDim3 (fakeDim3) int64 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ...

Data variables:

l3m_qual (fakeDim2, fakeDim3) uint8 255 255 255 255 255 255 255 255 255 ...

l3m_data (fakeDim0, fakeDim1) uint16 65535 65535 65535 65535 65535 ...

Attributes:

Latitude_Step: [ 0.04166667]

Start_Year: [2002]

Map_Projection: Equidistant Cylindrical

Title: MODISA Level-3 Standard Mapped Image

SW_Point_Latitude: [-89.97916412]

Start_Time: 2002365123005000

Start_Day: [365]

Mission:

Easternmost_Longitude: [ 180.]

Longitude_Units: degrees East

Units: deg-C

Scaled_Data_Maximum: [ 45.]

Station_Name:

Sensor:

Input_Files: A2003001.L3b_DAY_NSST.main

Period_Start_Day: [1]

Number_of_Lines: [4320]

Sensor_Name: MODISA

Period_End_Year: [2003]

Scaled_Data_Minimum: [-2.]

End_Year: [2003]

Longitude_Step: [ 0.04166667]

L2_Flag_Names: LAND,~HISOLZ

End_Millisec: [8704000]

Processing_Time: 2006068023708000

Intercept: [-2.]

Product_Name: A2003001.L3m_DAY_NSST_4

Scaling: linear

Software_Name: smigen

Software_Version: 3.30

Processing_Control: smigen par=A2003001.L3m_DAY_NSST_4.param

Period_End_Day: [1]

Parameter: Sea Surface Temperature

Orbit: [0]

Mission_Characteristics:

SW_Point_Longitude: [-179.97917175]

Start_Orbit: [0]

Station_Latitude: [ 0.]

Data_Bins: [4241743]

Data_Center:

Product_Type: D

Scaling_Equation: (Slope*l3m_data) + Intercept = Parameter value

Start_Millisec: [45005000]

Slope: [ 0.00071718]

Southernmost_Latitude: [-90.]

End_Orbit: [0]

Period_Start_Year: [2003]

Replacement_Flag: ORIGINAL

Data_Maximum: [ 34.93000031]

Number_of_Columns: [8640]

Latitude_Units: degrees North

Station_Longitude: [ 0.]

Data_Minimum: [-1.99999905]

Northernmost_Latitude: [ 90.]

Westernmost_Longitude: [-180.]

End_Time: 2003002022504000

Measure: Mean

End_Day: [2]

Sensor_Characteristics:

Cheers,

Stephan

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