I want to download Black Marble daily nighttime lights (NTL) using Google Earth Engine (GEE). My question is if the pixel values of the images are in digital numbers (DN) or radiance. Here is a link to GEE NTL product (https://developers.google.com/earth-engine/datasets/catalog/NOAA_VIIRS_001_VNP46A2#bands).
The values are in nano watts per square centimeter per steradian nW/(cm^2 -sr).
1. According to the documentation for the "NOAA/VIIRS/001/VNP46A2" dataset in Google Earth Engine, the pixel values of the Black Marble nighttime lights (NTL) images are represented as Digital Numbers (DN), also known as digital counts.
Digital Numbers are raw sensor measurements that have not been converted to physical units such as radiance or reflectance. In the case of the Black Marble dataset, the DN values represent the brightness or intensity of nighttime lights captured by the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor.
2. You can find this information in the dataset documentation on the Earth Engine Data Catalog page for the "NOAA/VIIRS/001/VNP46A2" dataset, specifically under the "bands" section. Each band in the dataset is described, including its name and data type. In this case, the bands mentioned are "cf_cvg", "DN", and "QF" for cloud-free coverage, DN values, and quality flags, respectively.
To download and work with the Black Marble nighttime lights data in Google Earth Engine, you can use the dataset mentioned above. The DN values can be converted to radiance or other physical units using calibration coefficients specific to the VIIRS instrument. These coefficients can be obtained from the instrument's calibration documentation or related scientific publications.
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