This readme file was generated on [2024-08-02] by [Martin Wieser]
Version 2 updated on [2024-10-02] by [Martin Wieser]
Version 3 updated on [2025-02-13] by [Martin Wieser]

GENERAL INFORMATION

Title of Dataset:  
Negative ion mass spectrum from observations by the Negative Ion at the Lunar 
Surface (NILS) instrument onboard of the Chang'E-6 lunar lander. 


Author/Principal Investigator Information

Name: Martin Wieser
ORCID: 0000-0002-1760-210X
Institution: Swedish Institute of Space Physics
Address: Bengt Hultqvists väg 1, 981 92 Kiruna, Sweden
Email: wieser@irf.se


Author/Principal Investigator Information

Name: Aibing Zhang
Institution: National Space Science Center (NSSC), Chinese Academy of Sciences (CAS)
Address: No. 1 Nanertiao, Zhongguancun, Haidian district, Beijing, 100190, China
Email: zhab@nssc.ac.cn


Date of data collection: 2024-06-02T03:01:53.00 UTC to 2024-06-03T03:37:35.021 UTC
Geographic location of data collection: 

Moon, lunar surface, 153.978°W, 41.638°S based on Chang'E-2 derived coordinates 
or 153.986°W, 41,638°S based on Lunar Reconnaissance Orbiter derived coordinates


Information about funding sources that supported the collection of the data: 

The Negative Ions on the Lunar Surface (NILS) instrument was developed by the 
Swedish Institute of Space Physics (IRF) in Kiruna, Sweden, on behalf of the 
European Space Agency (ESA). It was supported by the ESA grant No. 3-17483/22/NL/DB. 



SHARING/ACCESS INFORMATION

Licenses/restrictions placed on the data: 
CC BY-NC-SA 4.0

Licenses/restrictions placed on the code: 
Apache License, Version 2.0

Links to publications that cite or use the data: 
n/a


Links to other publicly accessible locations of the data: 
n/a



Recommended citation for this dataset: 

Wieser, M., & Zhang, A. (2025). Negative ion mass spectrum from observations by the 
Negative Ion at the Lunar Surface (NILS) instrument onboard of the Chang’E-6 lunar 
lander. (Version 3) [Data set]. Swedish Institute of Space Physics.




DATA & FILE OVERVIEW


File List:

(1)  nils_exm_matrix_surface.csv

Time and viewing direction integrated energy - mass matrix. The data contains the 
number of time-of-flight coincidence counts for each mass- and energy bin combination
summed up over the data collection interval for viewing directions pointing more than 
5 degrees below the horizon. 



METHODOLOGICAL INFORMATION

Description of methods used for collection/generation of data: 

The data was recorded by the Negative Ions at the Lunar surface (NILS) instrument 
onboard of the Chinese Chang'E-6 lunar lander while the lander was active on the 
lunar surface. A description of the NILS instrument and relevant instrument calibration 
data can be found here [1]:

[1] R. Canu-Blot, M. Wieser, M. Kerenyi, S. Barabash, X.-D. Wang, T.
Maynadie, A. Zhang, W. Wang, N. Melville, Q. Wang, Y. Zou, H. Dou, H.
Zhu, V. Alatalo, A. Edström, L. Kalla, S. Karlsson, M. Oja, J. Olsen,
J. Peterson, D. Stålnacke, and D. Upton. The Negative Ions at the
Lunar Surface (NILS) instrument on the Chang’E-6 mission. Research
Square, 2024. Preprint at https://doi.org/10.21203/rs.3.rs-4718105/v1.

The raw NILS data consists of a four-dimensional data set of time-of-flight 
coincidence events with dimensions: Time x Energy_bin x Viewing_direction x Mass_bin.  

The data is derived from the binary raw telemetry after decompression and summation
over time and viewing directions. Data where the NILS internal high voltages were on 
nominal levels and when the instrument field-of-view was pointing more than 5 degrees 
below the horizon towards the surface are included only. The time and viewing direction 
coordinates were summed up resulting in a two-dimensional matrix with dimensions of 
Energy_bin x Mass bin. A total of 172 energy-direction scans were summed.

Methods for processing the data:  

For each energy setting of the instrument (each row) in nils_exm_matrix_surface, 
the accumulmation time was 43.3 seconds. To convert this to flux, 
please refeer to Equation 76 in [1]. For this application, the geometric factor 
used is the elevation-integrated geometric factor (as given in Equation 71 in [1]) 
for the viewing directions: [ 4,  5,  6,  7, 12, 13, 14, 15], see Table 3 in [1].
Note that the mass spectrum (elements M00 to M63) are given in instrument 
internal mass units. To obtain masses in, e.g. units of amu, a linear combination of the 
mass response functions given in [1] must be fitted to the data, for example using a 
maximum likelihood fitting procedure.

Example python >=3.12 source code to read and process the data is provided in the compressed
archive nils_analysis.zip. See the file README.md in this archive for instructions. 


Standards and calibration information: 
Applicable energy levels and interpretation of the mass bins can be found in [1], see above.


People involved with sample collection, processing, analysis and/or submission: 
Martin Wieser
Romain Canu-Blot
Aibing Zhang
and the NILS instrument team



DATA-SPECIFIC INFORMATION FOR: nils_exm_matrix_surface.csv

Format: Float and Integer numbers, whitespace delimited, the first line is a comment

Number of variables: 1

Variable List: 
nils_exm_matrix_surface : 
     Shape:  48 (rows) x 65 (columns) 
     Rows: Mass spectra for the energy settings indicated by the first element.
     Columns: Instrument energy setting in eV, followed by the mass bin number 
         increasing from left (M00) to right (M63).
     Cells: Energy in eV or an integer number of coincidence events recorded for each mass bin.   

     