“ESTIMASI SEBARAN KUALITAS BATUBARA (ASH CONTENT) MENGGUNAKAN METODE INVERS DISTANCE WEIGHTED (IDW) DAN ORDINARY KRIGING (OK) DI PT. KAYAN PUTRA UTAMA COAL SITE SEPARI, KALIMANTAN TIMUR”. 2019. GEOSAINS KUTAI BASIN 2 (1). https://doi.org/10.30872/geofisunmul.v2i1.330.