Hyrax Error 400 when trying to access Daymet via opendap.earthdata.nasa.gov

[mehdi mehdizadeh]

Hello OPeNDAP Support Team,

I’m getting a Hyrax – Bad Request (400) when I try to open a Daymet URL on the Earthdata Hyrax host.

• What I tried (URL):
  https://opendap.earthdata.nasa.gov/thredds/ncss/ornldaac/2129.dmr.html

• Expected: View or subset Daymet (V4 daily) data via OPeNDAP/NCSS.

• Actual: “Hyrax – Bad Request (400)” with message indicating a poorly formed DAP request URL.

My account details

• Earthdata Login username: mehdi_1359

• Contact email: mehdiza...@yahoo.com

Environment

• OS: Windows 10 (64-bit)

• Browser: Chrome 141

• Time of error: [add local date/time]

• I can browse and download the same Daymet files successfully from the ORNL DAAC THREDDS host (https://thredds.daac.ornl.gov/thredds/fileServer/ornldaac/2129/...). I’m writing to confirm whether the Earthdata Hyrax host supports Daymet at this path and, if so, what the correct OPeNDAP/NCSS endpoint should be.

Could you please advise the correct URL pattern (e.g., dodsC, ncss) for accessing Daymet on the Earthdata Hyrax server, or confirm that I should use the ORNL THREDDS host instead?

I can provide the full error text and a screenshot if helpful.

Thank you ,
Mehdi 

[Miguel Jimenez]

Hi Mehdi, 

Thank you for reaching out. NASA is currently migrating their data to the cloud, and as a result, many of the known OPeNDAP endpoints are changing with little to no notice. But we can help to find those OPeNDAP URLs. 

We provide some tutorial documentation that uses python to discover OPeNDAP URLs. The resource can be found on PyDAP’s official documentation, the url below: 

https://pydap.github.io/pydap/en/notebooks/GetCMRURLS.html

We recommend installing the most recent version of pydap (currently at 3.5.8). That documentation also has instructions on how to install pydap, along with some tutorials on how to access OPeNDAP data across many (potentially 100s) or individual OPeNDAP URLs.

The requirements you will need to find OPeNDAP urls are, at a minimum,

• The data product’s Concept Collection ID, or its DOI. You can find that on resources of the DAAC (ORNL), or Earthdata Search. I quickly looked at Daymet, daily, 4km resolution, and found the Concept Collection ID = C2532426483-ORNL_CLOUD.
• (Recommended) A time range for the data / analysis you are interested. This will narrow the search.

For example, running the following code

===========================================

from pydap.client import get_cmr_urls

import datetime as dt

# define concept collection id for 

ccid = "C2532426483-ORNL_CLOUD"

time_range = time_range = [dt.datetime(2021, 3, 1), dt.datetime(2021, 3, 31)]

urls = get_cmr_urls(ccid=ccid, time_range=time_range, limit=100)

============================================

On my machine the code above produced 21 distinct urls. Each file contains daily data for the whole 2021 year. And for example, an individual URL looks like:

https://opendap.earthdata.nasa.gov/collections/C2532426483-ORNL_CLOUD/granules/Daymet_Daily_V4R1.daymet_v4_daily_na_tmax_2021.nc

As you may have noticed, the data is no longer on a Thredds server, instead is on a Hyrax data server. This is a DAP4 OPeNDAP server  that is running on the cloud. To access the data response in the DAP4 protocol you can add a `.dmr ` at the end of the URL above, and navigate to that page. NOTE that a DAP4 OPeNDAP server is fully backwards compatible with the DAP2 protocol, and so you can still request a DAP2 responses (DDS,DDAS , DODS), and overall should provide a similar feel.

* If you do not feel comfortable install python packages, you can run some tutorials we have curated, interactively on a browser. All dependencies required to run those are pre-installed. To navigate to this interactive environment you need to you to the Official OPeNDAP Github repository for NASA-tutorials, and select a black and blue badge button called: launch Binder. Below is the url to that resource where you can find the Binder Badge.

https://github.com/OPENDAP/NASA-tutorials

This will take to you an interactive environment where will be able to run python code on Jupyter notebooks on a browser. One of the few tutorials there, demonstrates how to discover OPeNDAP URLs from NASA, and you can modify them as you like.

Thank you very much for reaching out,

Miguel Jimenez-Urias, PhD
Computational Oceanographer | Sc. Community Director
OPeNDAP, Inc

https://www.linkedin.com/in/MiguelJimenezUrias/

On Oct 9, 2025, at 6:49 AM, 'mehdi mehdizadeh' via User Support <sup...@opendap.org> wrote:

Daymet (V4 daily)