astro-legacy-archive/cobe-dmr-pixelized-differential-data

COBE DMR four-year pixelized differential data

The preview bins the 31A source rows by their ordered PIX_PLUS and PIX_MINU identities; colour records the number of source rows in each 24 by 24 pixel bin.

Regenerate it from the published Parquet data with python tools/render_hub_preview.py cobe-dmr-pixelized-differential-data datasets/cobe-dmr-pixelized-differential-data/preview.png.

This dataset contains the COBE Differential Microwave Radiometer four-year Pixelized Differential Data Project Data Set served by LAMBDA. Six detector channels at 31.5, 53, and 90 GHz are delivered as eight source files because 31B is split into three source time intervals.

python -m venv .venv && .venv/bin/pip install datasets huggingface_hub pyarrow

from datasets import load_dataset
dataset = load_dataset("astro-legacy-archive/cobe-dmr-pixelized-differential-data", "DMR_PIXDIFF_31A_4YR", split="train[:1]", columns=["PIX_PLUS", "PIX_MINU", "SUM"])
row = dataset[0]
print(row["PIX_PLUS"], row["PIX_MINU"], row["SUM"])

0 325 325.0431823730469

import json
from huggingface_hub import hf_hub_download
import pyarrow.parquet as pq
path = hf_hub_download("astro-legacy-archive/cobe-dmr-pixelized-differential-data", "DMR_PIXDIFF_31A_4YR.parquet", repo_type="dataset")
meta = json.loads(pq.read_schema(path).metadata[b"explicit_pixel_table"])
print([field["name"] for field in meta["pixelisation"]["pixel_columns"]])

['PIX_PLUS', 'PIX_MINU']

Dataset structure

Each configuration is one source DMR_PIXPERM binary table. The seven scalar fields remain in source order: int16 PIX_PLUS, int16 PIX_MINU, int32 N_OBS, and float32 SUM, SUM_2, SUM_3, and SUM_4. The source units are respectively blank, blank, blank, mK, mK**2, mK**3, and mK**4; blank TUNIT cards are preserved as present and blank.

Rows describe source pixel permutations. PIX_PLUS and PIX_MINU each span 0 through 6,143 and neither is independently unique. Their ordered source pair is unique within each file and is recorded by schema 1.1 without adding a combined identifier column. The source rows remain sorted by PIX_PLUS and then PIX_MINU.

N_OBS is the number of observations accumulated for that permutation. SUM through SUM_4 retain the source sums of the first through fourth powers of the calibrated differential antenna temperature. No mean, variance, map value, coordinate, or decoded statistic is derived.

Pixelisation and observing periods

The primary headers state COORDSYS='E' and PIXRESOL=6. The pinned COBE document identifies the quadrilateralized spherical cube (CSC) projection; LAMBDA describes the sign as temperature in horn 1 minus temperature in horn 2. The documented 6,144-pixel identity on each side gives 37,748,736 possible ordered pairs. Missing pairs remain absent rows rather than archive fill values.

The primary headers retain channel, frequency, antenna-temperature scale, thermodynamic conversion, observation dates, noise measurements, correction flags, and removed-dipole parameters. The three 31B configurations are the three source time intervals and are not concatenated or renamed.

Source guidance and limitations

The four-year DMR Explanatory Supplement identifies the three 31B files as separate, unweighted intervals A, B, and C because coadding their pixelized differential data is not straightforward. Intervals B and C have higher RMS noise than interval A following a discontinuous increase in the receiver noise. They should not be treated as directly coaddable equal-noise parts.

Eclipse-season systematic errors significantly affect the 31 GHz channels; the released 31A and 31B products exclude the affected date ranges. Scientific use must also account for the documented calibration uncertainties and systematic-error limits rather than treating the corrected sums as free of those limitations.

Every source FITS header gives the dipole-restoration prescription. To restore the removed dipole to SUM for a pixel permutation, add N_OBS times the dot product of the header's dipole vector with the pointing vector for PIX_PLUS minus the pointing vector for PIX_MINU. The applicable DIP_MAG, DIP_ELON, and DIP_ELAT values remain in each embedded primary header; the header warns that this is neither a definitive DMR dipole nor the best-fit dipole from the dataset.

Provenance and reconstruction

The LAMBDA download table serves the eight FITS files. Together they contain 12,834,908 rows and occupy 308,165,760 bytes. Individual source and Parquet SHA-256 values are recorded in facts.yaml and each Parquet file embeds its own source pin. The four-year DMR Explanatory Supplement is the governing document for these four-year Project Data Sets.

The explicit_pixel_table metadata contains both complete FITS headers, source field definitions, ordered pixel identity, pixelisation statements and bases, physics, credit, and the fixed regeneration command. Rebuild with python tools/make_cobe_dmr_pixelized_differential_data.py data/cobe-dmr-pixelized-differential-data.

No explicit licence identifier is published. Preserve the COBE credit: “The COBE datasets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group.”

Licence

HEASARC states verbatim:

HEASARC materials are all available freely for your use.

This is a free-use statement rather than a named formal licence.

Errata and requests

To report an erratum, propose a correction, or ask a question about this dataset, open a Discussion or Pull Request in its Community tab; posting requires a free Hugging Face account. Dataset requests and archive-wide questions may be posted in the README space's Community tab or the Community tab of any dataset. Confirmed corrections are made in the source conversion tools and published by rebuilding the dataset.