fix refs typo

References.md

@@ -7,7 +7,7 @@ The material in this tutorial was developed with the aid of many online resource
 - RGI 7.0 Consortium, 2023. Randolph Glacier Inventory - A Dataset of Global Glacier Outlines, Version 7.0. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi:10.5067/f6jmovy5navz. Online access: https://doi.org/10.5067/f6jmovy5navz
 - [Alaska Satellite Facility Sentinel-1 On-Demand](https://search.asf.alaska.edu/#/?topic=onDemand)
 - [Micrsoft Planetary Computer Sentinel-1 RTC data](https://planetarycomputer.microsoft.com/dataset/sentinel-1-rtc)
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 ## Synthetic Aperture Radar resources
 - [The SAR Handbook](https://ntrs.nasa.gov/api/citations/20190002563/downloads/20190002563.pdf)
 - [ASF Sentinel-1 RTC Product Guide](https://hyp3-docs.asf.alaska.edu/guides/rtc_product_guide/)