Changed JPG to PNG and satellite height

I've changed the last line which saves the image from JPG format to PNG in order to be compatible with receive_meteor.sh script. I've also changed satellite height to 830 km since according to https://www.n2yo.com/satellite/?s=40069 perigee is 826.8 km, and apogee is 833.6 km as of 14 October 2020.

rectify.py

@@ -8,7 +8,7 @@ from math import atan,sin,cos,sqrt,tan,acos,ceil
 from PIL import Image
 
 EARTH_RADIUS = 6371.0
-SAT_HEIGHT = 822.5
+SAT_HEIGHT = 830.0
 SAT_ORBIT_RADIUS = EARTH_RADIUS + SAT_HEIGHT
 SWATH_KM = 2800.0
 THETA_C = SWATH_KM / EARTH_RADIUS
@@ -180,4 +180,4 @@ if __name__ == "__main__":
     # It's a dead pool now
     p.join()
 
-    rectified_img.save(out_fname + ".jpg", "JPEG", quality=90)
+    rectified_img.save(out_fname + ".png", "PNG")